Fix for crash of "mysql-test-run --debug mysqldump": don't access dir->str if dir is null.

sql/parse_file.cc:
  since recently, the "dir" parameter can be 0.

sql/parse_file.cc

@@ -224,7 +224,8 @@ sql_create_definition_file(const LEX_STRING *dir, const LEX_STRING *file_name,
   File_option *param;
   DBUG_ENTER("sql_create_definition_file");
   DBUG_PRINT("enter", ("Dir: %s, file: %s, base 0x%lx",
-		       dir->str, file_name->str, (ulong) base));
+		       dir ? dir->str : "(null)",
+                       file_name->str, (ulong) base));
 
   if (dir)
   {