yet more S_unexplored

Revert part of one of the earlier S_unexplored changes (erasing
the map window on tty) and deal with the issue differently.

src/display.c

@@ -1606,7 +1606,6 @@ int x, y, glyph;
         }                                \
     }
 
-static const gbuf_entry nul_gbuf = { 1, GLYPH_UNEXPLORED };
 /*
  * Turn the 3rd screen into UNEXPLORED that needs to be refreshed.
  */
@@ -1614,7 +1613,14 @@ void
 clear_glyph_buffer()
 {
     register int x, y;
-    register gbuf_entry *gptr;
+    register gbuf_entry *gptr, nul_gbuf;
+    int ch = ' ', color = NO_COLOR;
+    unsigned special = 0;
+
+    (void) mapglyph(GLYPH_UNEXPLORED, &ch, &color, &special, 0, 0, 0);
+    nul_gbuf.gnew = (ch != ' ' || color != NO_COLOR
+                     || (special & ~MG_UNEXPL) != 0) ? 1 : 0;
+    nul_gbuf.glyph = GLYPH_UNEXPLORED;
 
     for (y = 0; y < ROWNO; y++) {
         gptr = &g.gbuf[y][0];

win/tty/wintty.c

@@ -1652,16 +1652,12 @@ winid window;
         g.context.botlx = 1;
         break;
     case NHW_MAP:
-        /* the full map isn't erased often so the benefit of clearing the
+        /* cheap -- clear the whole thing and tell nethack to redraw botl */
-           whole screen and then redrawing status would be minimal here */
+        g.context.botlx = 1;
-        docorner(1, ROWNO - 1); /* sets map cells to S_unexplored
+        /*FALLTHRU*/
-                                 * which might not be <space> */
-        break;
     case NHW_BASE:
         clear_screen();
-        if (!g.program_state.gameover)
+        /* [this should reset state for MESSAGE, MAP, and STATUS] */
-            g.context.botlx = 1;
-        /* [this sould also reset state for MESSAGE, MAP, and STATUS] */
         break;
     case NHW_MENU:
     case NHW_TEXT: