R1:b88a87c43a28

Address a transaction issue with some audit actions not applying correctly

Summary:
See <https://discourse.phabricator-community.org/t/cannot-accept-commits-in-audit/2166/>.

In D19842, I changed `PhabricatorEditField->shouldGenerateTransactionsFromComment()`.

- Previously, it bailed on `getIsConduitOnly()`.
- After the patch, it bails on a missing `getCommentActionLabel()`.

The old code was actually wrong, and it was previously possible to apply possibly-invalid actions in some cases (or, at least…