Correct a straggling CLI format string after ref selector changes

Summary: Ref T13589. This is missing a "%s" conversion.

Test Plan: Will view a commit with a diff.

Maniphest Tasks: T13589

Differential Revision: https://secure.phabricator.com/D21512

src/applications/diffusion/query/rawdiff/DiffusionGitRawDiffQuery.php

@@ -23,7 +23,7 @@ final class DiffusionGitRawDiffQuery extends DiffusionRawDiffQuery {
       // Check if this is the root commit by seeing if it has parents, since
       // `git diff X^ X` does not work if "X" is the initial commit.
       list($parents) = $repository->execxLocalCommand(
-        'log -n 1 %s --',
+        'log -n 1 %s %s --',
         '--format=%P',
         gitsprintf('%s', $commit));