Fixes for degenerate RNG

Assume a degenerate RNG that always returns the same number.
With these fixes, the game starts and is almost playable.
There are still some places that will go into infinite loop, eg.
the mines level generation.

src/mklev.c

@@ -812,6 +812,7 @@ makelevel()
 
     /* for each room: put things inside */
     for (croom = g.rooms; croom->hx > 0; croom++) {
+        int trycnt = 0;
         if (croom->rtype != OROOM)
             continue;
 
@@ -833,7 +834,7 @@ makelevel()
         x = 8 - (level_difficulty() / 6);
         if (x <= 1)
             x = 2;
-        while (!rn2(x))
+        while (!rn2(x) && (++trycnt < 1000))
             mktrap(0, 0, croom, (coord *) 0);
         if (!rn2(3))
             (void) mkgold(0L, somex(croom), somey(croom));
@@ -1121,6 +1122,7 @@ coord *mp;
     if (g.nroom == 0) {
         mazexy(mp); /* already verifies location */
     } else {
+        int cnt = 0;
         /* not perfect - there may be only one stairway */
         if (g.nroom > 2) {
             int tryct = 0;
@@ -1135,9 +1137,9 @@ coord *mp;
         do {
             if (!somexy(croom, mp))
                 impossible("Can't place branch!");
-        } while (occupied(mp->x, mp->y)
+        } while ((occupied(mp->x, mp->y)
                  || (levl[mp->x][mp->y].typ != CORR
-                     && levl[mp->x][mp->y].typ != ROOM));
+                     && levl[mp->x][mp->y].typ != ROOM)) && (++cnt < 1000));
     }
     return croom;
 }