'Fix' an assertion failure during play: accidentally connecting a

long chain to a square numbered so low that the start of the chain
would have to go into negative numbers should not crash the game,
particularly when it happens as a momentary in-passing illustration.

I've fixed it for the moment just by removing the assertion. There's
probably a better fix which causes something less strange to happen
to the display as a result.

[originally from svn r8867]

signpost.c

@@ -1834,7 +1834,7 @@ static void tile_redraw(drawing *dr, game_drawstate *ds, int tx, int ty,
     /* Draw text (number or set). */
 
     if (num != 0) {
-        assert(num > 0);
+        /* assert(num > 0); - actually, no, this obstructs legal play */
         if (set == 0) {
             sprintf(buf, "%d", n);
         } else {