R1:bb16a1b0e2a8

Fix a possible fatal on the first push to a cluster repository

Summary:
Fixes T11020. I think this resolves things -- `$new_version` (set above) should be used, not `$new_log` directly.

Specifically, we would get into trouble if the initial push failed for some reason (working copy not initialized yet, commit hook rejected, etc).

Test Plan: Made a bad push to a new repository. Saw it freeze before the patch and succeed afterwards.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11020…