Do not swallow the exceptions from the input iter.

Author: lichray

pymongo/_cmessagemodule.c

@@ -216,6 +216,12 @@ static PyObject* _cbson_insert_message(PyObject* self, PyObject* args) {
  }
  Py_DECREF(iterator);
 
+ if (PyErr_Occurred()) {
+ buffer_free(buffer);
+ PyMem_Free(collection_name);
+ return NULL;
+ }
+
  if (!max_size) {
  PyObject* InvalidOperation = _error("InvalidOperation");
  PyErr_SetString(InvalidOperation, "cannot do an empty bulk insert");