Only pop metrics if it exists

Author: nevillelyh

Diff for: python/coglet/file_runner.py

@@ -214,7 +214,8 @@ async def _predict(self, pid: str, req: Dict[str, Any]) -> None:
         finally:
             resp['completed_at'] = util.now_iso()
         self._respond(pid, epoch, resp)
-        scope.metrics.pop(pid)
+        if pid in scope.metrics:
+            scope.metrics.pop(pid)
         epoch += 1
 
     def _respond(