chore: partial revert of PR #357

This reverts commit e120a0c.

Author: parthea

google/api_core/bidi.py

@@ -92,7 +92,10 @@ def _is_active(self):
         # Note: there is a possibility that this starts *before* the call
         # property is set. So we have to check if self.call is set before
         # seeing if it's active.
-        return self.call is not None and self.call.is_active()
+        if self.call is not None and not self.call.is_active():
+            return False
+        else:
+            return True
 
     def __iter__(self):
         if self._initial_request is not None: