Avoid unbound local on exception. Fixes #1686154

Author: adustman

MySQLdb/MySQLdb/cursors.py

@@ -158,6 +158,7 @@ def execute(self, query, args=None):
         if args is not None:
             query = query % db.literal(args)
         try:
+            r = None
             r = self._query(query)
         except TypeError, m:
             if m.args[0] in ("not enough arguments for format string",