[promptflow][BugFix] Check bulk result first before get metrics (#584)

# Description

Executor might exit abnormally in some cases, then `bulk_result` will be
`None` so we will run into error. This PR adds check first to avoid such
error.

# All Promptflow Contribution checklist:
- [X] **The pull request does not introduce [breaking changes]**
- [X] **CHANGELOG is updated for new features, bug fixes or other
significant changes.**
- [X] **I have read the [contribution guidelines](../CONTRIBUTING.md).**

## General Guidelines and Best Practices
- [X] Title of the pull request is clear and informative.
- [X] There are a small number of commits, each of which have an
informative message. This means that previously merged commits do not
appear in the history of the PR. For more information on cleaning up the
commits in your PR, [see this
page](https://github.com/Azure/azure-powershell/blob/master/documentation/development-docs/cleaning-up-commits.md).

### Testing Guidelines
- [ ] Pull request includes test coverage for the included changes.

Author: zhengfeiwang

src/promptflow/CHANGELOG.md

@@ -10,6 +10,7 @@
 - [Flow build] Fix flow build file name and environment variable name when connection name contains space.
 - Reserve `.promptflow` folder when dump run snapshot.
 - Read/write log file with encoding specified.
+- Avoid inconsistent error message when executor exits abnormally.
 
 ### Other Changes
 - [Executor][Internal] Improve error message with more details and actionable information.

src/promptflow/promptflow/_sdk/operations/_run_submitter.py

@@ -316,7 +316,7 @@ def _submit_bulk_run(self, flow: Flow, run: Run, local_storage: LocalStorageOper
             # exceptions
             local_storage.dump_exception(exception=exception, bulk_results=bulk_result)
             # system metrics: token related
-            system_metrics = bulk_result.get_openai_metrics()
+            system_metrics = {} if bulk_result is None else bulk_result.get_openai_metrics()
 
             self.run_operations.update(
                 name=run.name,