Ignore unset hub/group/project field on backend

In some cases, backends can be created without the `_instance` field
set (so it is `None`). In this case, it is better to ignore the field
than to raise an uncaught exception.

qiskit_experiments/framework/experiment_data.py

@@ -587,7 +587,7 @@ def _set_backend(self, new_backend: Backend, recursive: bool = True) -> None:
         if provider is not None:
             self._set_hgp_from_provider(provider)
         # qiskit-ibm-runtime style
-        elif hasattr(self._backend, "_instance"):
+        elif hasattr(self._backend, "_instance") and self._backend._instance:
             self.hgp = self._backend._instance
         if recursive:
             for data in self.child_data():