make sure to close debug log when closing collection

anki/collection.py

@@ -161,6 +161,7 @@ crt=?, mod=?, scm=?, dty=?, usn=?, ls=?, conf=?""",
             self.db.close()
             self.db = None
             self.media.close()
+            self._closeLog()
 
     def reopen(self):
         "Reconnect to DB (after changing threads, etc)."