lev_comp: Show error when map height exceeds temp buffer size

Before, it would just segfault.  Now, it shows an informative message,
then segfaults, which still isn't great but is better than nothing.

Incidentally, I hit this when porting the new Ranger quest map from
dNetHack, since it has # comments within the MAP-ENDMAP segment that
would cause the map reader to freak out; I moved them outside for the
port.

libnitrohack/util/lev_main.c

@@ -874,6 +874,8 @@ void scan_map(char *map, sp_lev *sp)
 
 	/* Then parse it now */
 	while (map && *map) {
+		if (max_hig >= ROWNO)
+			lc_error("Map too tall, max is %d", ROWNO);
 		tmpmap[max_hig] = malloc(max_len);
 		s1 = strchr(map, '\n');
 		if (s1) {