Don't barf on bad commit identifiers

Summary:
If someone provides an invalid svn rev number (like providing a git commit
hash instead) for a diffusion commit, we should ignore it like we ignore
other bad input to DiffusionCommitQuery, instead of barfing.

Test Plan:
put an invalid blame rev with rEsomehash (where E is an svn repo), and
differential loads.

Reviewers: epriestley, wez

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D5389

src/applications/diffusion/query/DiffusionCommitQuery.php

@@ -112,6 +112,9 @@ final class DiffusionCommitQuery
           }
 
           if ($repo->isSVN()) {
+            if (!ctype_digit($ref['identifier'])) {
+              continue;
+            }
             $sql[] = qsprintf(
               $conn_r,
               '(repositoryID = %d AND commitIdentifier = %d)',