fix #H2642 - escaping from drowning by moving diagonally

From a bug report, you could crawl
out of water to avoid drowning by moving diagonally into an intact doorway
even though regular movement won't allow that.  (Second version of Medusa's
level has a door adjacent to water.)  You could also escape diagonally when
polymorphed into a grid bug.

src/hack.c

@@ -2390,6 +2390,28 @@ int x, y;
     return !(lev_p->doormask & ~(D_NODOOR|D_BROKEN));
 }
 
+/* used by drown() to check whether hero can crawl from water to <x,y> */
+boolean
+crawl_destination(x, y)
+int x, y;
+{
+    /* is location ok in general? */
+    if (!goodpos(x, y, &youmonst, 0)) return FALSE;
+
+    /* orthogonal movement is unrestricted when destination is ok */
+    if (x == u.ux || y == u.uy) return TRUE;
+
+    /* diagonal movement has some restrictions */
+    if (NODIAG(u.umonnum)) return FALSE;	/* poly'd into a grid bug... */
+    if (Passes_walls) return TRUE;		/* or a xorn... */
+    /* pool could be next to a door, conceivably even inside a shop */
+    if (IS_DOOR(levl[x][y].typ) && (!doorless_door(x, y) || block_door(x, y)))
+	return FALSE;
+    /* finally, are we trying to squeeze through a too-narrow gap? */
+    return !(bad_rock(youmonst.data, u.ux, y) &&
+	     bad_rock(youmonst.data, x, u.uy));
+}
+
 /* something like lookaround, but we are not running */
 /* react only to monsters that might hit us */
 int