Menu parser: fix possible infinite loop when loading menu file

When a #include is used, the file is searched in many places; when
the file was searched in the ':'-separated list of path it could
led to infinite loop if the list contained more than one path and
that the file was not found in the first path, the ':' separator
was not properly passed over.

WINGs/menuparser.c

@@ -493,6 +493,9 @@ static Bool menu_parser_include_file(WMenuParser parser)
 
 				fh = fopen(fullfilename, "rb");
 				if (fh != NULL) goto found_valid_file;
+
+				if (*src == ':')
+					src++;
 			}
 		}
 		WMenuParserError(parser, _("could not find file \"%s\" for include"), req_filename);