Error instead of crashing if no regions can be found

overviewer.py

@@ -405,7 +405,11 @@ dir but you forgot to put quotes around the directory, since it contains spaces.
         else:
             tex = texcache[texopts_key]
     
+        try:
             rset = w.get_regionset(render['dimension'][1])
+        except IndexError:
+            logging.error("Sorry, I can't find anything to render!  Are you sure there are .mca files in the world directory?")
+            return 1
         if rset == None: # indicates no such dimension was found:
             logging.error("Sorry, you requested dimension '%s' for %s, but I couldn't find it", render['dimension'][0], render_name)
             return 1