Small fix to prevent a division by zero.

server/render.c

@@ -208,7 +208,7 @@ render_frame (LinkedList * list,
 				screenlist_action = 0;
 		}
 
-		fy %= fhgt;
+		if (fhgt == 0) { fy = 0; } else { fy %= fhgt; }
 		if (fy > fhgt - vis_height)
 			fy = fhgt - vis_height;