Fix traps generated inside walls

When fuzzing, noticed a trap generated inside a wall. Culprit
was one of the themed rooms that generates a rectangular room and then
puts freestanding wall columns inside.  Note in somexy that it can
return a non-accessible location, and change the places that used
it and absolutely needed a space to somexyspace.

src/mklev.c

@@ -1478,7 +1478,7 @@ mktrap(
                 return;
             if (mktrapflags & MKTRAP_MAZEFLAG)
                 mazexy(&m);
-            else if (!somexy(croom, &m))
+            else if (!somexyspace(croom, &m))
                 return;
         } while (occupied(m.x, m.y)
                  || (avoid_boulder && sobj_at(BOULDER, m.x, m.y)));
@@ -1778,7 +1778,7 @@ find_okay_roompos(struct mkroom *croom, coord *crd)
     do {
         if (++tryct > 200)
             return FALSE;
-        if (!somexy(croom, crd))
+        if (!somexyspace(croom, crd))
             return FALSE;
     } while (occupied(crd->x, crd->y) || bydoor(crd->x, crd->y));
     return TRUE;

src/mkroom.c

@@ -281,7 +281,7 @@ fill_zoo(struct mkroom* sroom)
         }
         i = 100;
         do { /* don't place throne on top of stairs */
-            (void) somexy(sroom, &mm);
+            (void) somexyspace(sroom, &mm);
             tx = mm.x;
             ty = mm.y;
         } while (occupied((coordxy) tx, (coordxy) ty) && --i > 0);
@@ -294,7 +294,7 @@ fill_zoo(struct mkroom* sroom)
         if (sroom->irregular) {
             /* center might not be valid, so put queen elsewhere */
             if ((int) levl[tx][ty].roomno != rmno || levl[tx][ty].edge) {
-                (void) somexy(sroom, &mm);
+                (void) somexyspace(sroom, &mm);
                 tx = mm.x;
                 ty = mm.y;
             }
@@ -403,7 +403,7 @@ fill_zoo(struct mkroom* sroom)
     case COURT: {
         struct obj *chest, *gold;
         levl[tx][ty].typ = THRONE;
-        (void) somexy(sroom, &mm);
+        (void) somexyspace(sroom, &mm);
         gold = mksobj(GOLD_PIECE, TRUE, FALSE);
         gold->quan = (long) rn1(50 * level_difficulty(), 10);
         gold->owt = weight(gold);
@@ -667,6 +667,10 @@ inside_room(struct mkroom* croom, coordxy x, coordxy y)
                       && y >= croom->ly - 1 && y <= croom->hy + 1);
 }
 
+/* return a coord c inside mkroom croom, but not in a subroom.
+   returns TRUE if any such space found.
+   can return a non-accessible location, eg. inside a wall
+   if a themed room is not irregular, but has some non-room terrain */
 boolean
 somexy(struct mkroom* croom,coord * c)
 {
@@ -716,6 +720,7 @@ somexy(struct mkroom* croom,coord * c)
     return TRUE;
 }
 
+/* like somexy(), but returns an accessible location */
 boolean
 somexyspace(struct mkroom* croom, coord *c)
 {

src/teleport.c

@@ -500,7 +500,7 @@ vault_tele(void)
     register struct mkroom *croom = search_special(VAULT);
     coord c;
 
-    if (croom && somexy(croom, &c) && teleok(c.x, c.y, FALSE)) {
+    if (croom && somexyspace(croom, &c) && teleok(c.x, c.y, FALSE)) {
         teleds(c.x, c.y, TELEDS_TELEPORT);
         return;
     }
@@ -1465,7 +1465,7 @@ mvault_tele(struct monst* mtmp)
     struct mkroom *croom = search_special(VAULT);
     coord c;
 
-    if (croom && somexy(croom, &c) && goodpos(c.x, c.y, mtmp, 0)) {
+    if (croom && somexyspace(croom, &c) && goodpos(c.x, c.y, mtmp, 0)) {
         rloc_to(mtmp, c.x, c.y);
         return;
     }