Fix mention_map and hiders causing a light source error

Prevent glyph change messages while loading a level file.
Otherwise a monster hiding under an item triggered a vision recalc
before light sources were linked to their sources, leading into
strange errors looking like pointer corruption.

getlev -> hide_monst -> hideunder -> newsym -> show_glyph ->
 pline_xy -> vision_recalc -> do_light_sources -> get_obj_location

Add in_getlev program state variable, analogous to in_mklev

include/hack.h

@@ -766,6 +766,7 @@ struct sinfo {
     int exiting;                /* an exit handler is executing */
     int saving;                 /* creating a save file */
     int restoring;              /* reloading a save file */
+    int in_getlev;              /* in getlev() */
     int in_moveloop;            /* normal gameplay in progress */
     int in_impossible;          /* reporting a warning */
     int in_docrt;               /* in docrt(): redrawing the whole screen */

src/display.c

@@ -1950,6 +1950,7 @@ show_glyph(coordxy x, coordxy y, int glyph)
 
     if (a11y.glyph_updates && !a11y.mon_notices_blocked
         && !gp.program_state.in_docrt
+        && !gp.program_state.in_getlev
         && (oldglyph != glyph || gg.gbuf[y][x].gnew)) {
         int c = glyph_to_cmap(glyph);
         if ((glyph_is_nothing(oldglyph) || glyph_is_unexplored(oldglyph)

src/restore.c

@@ -1005,6 +1005,8 @@ getlev(NHFILE *nhfp, int pid, xint8 lev)
     short tlev;
 #endif
 
+    gp.program_state.in_getlev = TRUE;
+
     if (ghostly)
         clear_id_mapping();
 
@@ -1233,6 +1235,7 @@ getlev(NHFILE *nhfp, int pid, xint8 lev)
 
     if (ghostly)
         clear_id_mapping();
+    gp.program_state.in_getlev = FALSE;
 }
 
 void

src/vision.c

@@ -521,7 +521,7 @@ vision_recalc(int control)
     int oldseenv;      /* previous seenv value */
 
     gv.vision_full_recalc = 0; /* reset flag */
-    if (gi.in_mklev || !iflags.vision_inited)
+    if (gi.in_mklev || gp.program_state.in_getlev || !iflags.vision_inited)
         return;
 
     /*