Add completely blank symbol set

The blank symbol set can be used with screen reader software
to prevent it from reading the map symbols.

Prevent a segfault when looking at the map and many symbols
share the same character. Don't list too many symbols when
looking at those, if many share the same character.

dat/symbols

@@ -386,6 +386,176 @@ start: NHAccess
 	S_explode9: \047
 finish
 
+# All symbols are spaces
+start: Blank
+	Description: Completely blank symbols
+        S_air: \032
+        S_altar: \032
+        S_amulet: \032
+        S_angel: \032
+        S_ant: \032
+        S_anti_magic_trap: \032
+        S_armor: \032
+        S_armour: \032
+        S_arrow_trap: \032
+        S_ball: \032
+        S_bars: \032
+        S_bat: \032
+        S_bear_trap: \032
+        S_blcorn: \032
+        S_blob: \032
+        S_book: \032
+        S_boomleft: \032
+        S_boomright: \032
+        S_boulder: \032
+        S_brcorn: \032
+        S_centaur: \032
+        S_chain: \032
+        S_cloud: \032
+        S_cockatrice: \032
+        S_coin: \032
+        S_corr: \032
+        S_crwall: \032
+        S_dart_trap: \032
+        S_demon: \032
+        S_digbeam: \032
+        S_dnladder: \032
+        S_dnstair: \032
+        S_dog: \032
+        S_dragon: \032
+        S_eel: \032
+        S_elemental: \032
+        S_explode1: \032
+        S_explode2: \032
+        S_explode3: \032
+        S_explode4: \032
+        S_explode5: \032
+        S_explode6: \032
+        S_explode7: \032
+        S_explode8: \032
+        S_explode9: \032
+        S_eye: \032
+        S_falling_rock_trap: \032
+        S_feline: \032
+        S_fire_trap: \032
+        S_flashbeam: \032
+        S_food: \032
+        S_fountain: \032
+        S_fungus: \032
+        S_gem: \032
+        S_ghost: \032
+        S_giant: \032
+        S_gnome: \032
+        S_golem: \032
+        S_grave: \032
+        S_gremlin: \032
+        S_hbeam: \032
+        S_hcdbridge: \032
+        S_hcdoor: \032
+        S_hodoor: \032
+        S_hole: \032
+        S_human: \032
+        S_humanoid: \032
+        S_hwall: \032
+        S_imp: \032
+        S_jabberwock: \032
+        S_jelly: \032
+        S_kobold: \032
+        S_kop: \032
+        S_land_mine: \032
+        S_lava: \032
+        S_leprechaun: \032
+        S_level_teleporter: \032
+        S_lich: \032
+        S_light: \032
+        S_litcorr: \032
+        S_lizard: \032
+        S_lslant: \032
+        S_magic_portal: \032
+        S_magic_trap: \032
+        S_mimic: \032
+        S_mimic_def: \032
+        S_mummy: \032
+        S_naga: \032
+        S_nymph: \032
+        S_ogre: \032
+        S_orc: \032
+        S_piercer: \032
+        S_pit: \032
+        S_poisoncloud: \032
+        S_polymorph_trap: \032
+        S_pool: \032
+        S_potion: \032
+        S_pudding: \032
+        S_quadruped: \032
+        S_quantmech: \032
+        S_ring: \032
+        S_rock: \032
+        S_rodent: \032
+        S_rolling_boulder_trap: \032
+        S_rslant: \032
+        S_rust_trap: \032
+        S_rustmonst: \032
+        S_scroll: \032
+        S_sink: \032
+        S_sleeping_gas_trap: \032
+        S_snake: \032
+        S_spider: \032
+        S_spiked_pit: \032
+        S_squeaky_board: \032
+        S_ss1: \032
+        S_ss2: \032
+        S_ss3: \032
+        S_ss4: \032
+        S_statue_trap: \032
+        S_stone: \032
+        S_sw_bc: \032
+        S_sw_bl: \032
+        S_sw_br: \032
+        S_sw_ml: \032
+        S_sw_mr: \032
+        S_sw_tc: \032
+        S_sw_tl: \032
+        S_sw_tr: \032
+        S_tdwall: \032
+        S_teleportation_trap: \032
+        S_throne: \032
+        S_tlcorn: \032
+        S_tlwall: \032
+        S_tool: \032
+        S_trap_door: \032
+        S_trapper: \032
+        S_trcorn: \032
+        S_tree: \032
+        S_troll: \032
+        S_trwall: \032
+        S_tuwall: \032
+        S_umber: \032
+        S_unicorn: \032
+        S_upladder: \032
+        S_upstair: \032
+        S_vampire: \032
+        S_vbeam: \032
+        S_vcdbridge: \032
+        S_vcdoor: \032
+        S_vibrating_square: \032
+        S_vodoor: \032
+        S_vortex: \032
+        S_vwall: \032
+        S_wand: \032
+        S_water: \032
+        S_weapon: \032
+        S_web: \032
+        S_worm: \032
+        S_worm_tail: \032
+        S_wraith: \032
+        S_xan: \032
+        S_xorn: \032
+        S_yeti: \032
+        S_zombie: \032
+        S_zruty: \032
+finish
+
 start: plain
 	Description: Same as Default symbols, except '+' for corner walls
 	S_tlcorn: '+'

src/pager.c

@@ -53,6 +53,8 @@ const char *new_str;
         return 0;
 
     space_left = BUFSZ - strlen(buf) - 1;
+    if (space_left < 1)
+        return 0;
     (void) strncat(buf, " or ", space_left);
     (void) strncat(buf, new_str, space_left - 4);
     return 1;
@@ -918,6 +920,10 @@ const char **firstmatch;
      * If we are looking at the screen, follow multiple possibilities or
      * an ambiguous explanation by something more detailed.
      */
+
+    if (found > 4)
+        Sprintf(out_str, "%s", "That can be many things");
+
  didlook:
     if (looked) {
         if (found > 1 || need_to_look) {