pull-requests: updates on pull requests that don't have versions shouldn't

throw any errors.

rhodecode/model/pull_request.py

@@ -637,7 +637,11 b' class PullRequestModel(BaseModel):'
             pull_request_version = self._create_version_from_snapshot(pull_request)
             self._link_comments_to_version(pull_request_version)
         else:
+            try:
             ver = pull_request.versions[-1]
+            except IndexError:
+                ver = None
+
             pull_request.pull_request_version_id = \
                 ver.pull_request_version_id if ver else None
             pull_request_version = pull_request