Allow DifferentialDiff to construct proper DifferentialChangeset objects from

diffs which add empty files

Summary:
See T507 and some others. We now parse empty git diffs correctly, but the logic
to build DifferentialDiffs out of them leaves the objects with 'null' for
$changesets, when it should be array().

Further layers later throw, believing we have not loaded the changesets, when we
actually have, there just aren't any.

Test Plan: Viewed rJX05d493e17fbbb29f29e4880be6834d1d7415374e in Diffusion,
which adds an empty README file. No exception thrown.

Reviewers: jungejason, nh, tuomaspelkonen, aran

Reviewed By: nh

CC: aran, nh

Differential Revision: 1038

src/applications/differential/storage/diff/DifferentialDiff.php

@@ -114,7 +114,9 @@ class DifferentialDiff extends DifferentialDAO {
       $changeset = new DifferentialChangeset();
       $add_lines = 0;
       $del_lines = 0;
-      foreach ($change->getHunks() as $hunk) {
+      $hunks = $change->getHunks();
+      if ($hunks) {
+        foreach ($hunks as $hunk) {
           $dhunk = new DifferentialHunk();
           $dhunk->setOldOffset($hunk->getOldOffset());
           $dhunk->setOldLen($hunk->getOldLength());
@@ -126,6 +128,10 @@ class DifferentialDiff extends DifferentialDAO {
           $del_lines += $hunk->getDelLines();
           $lines += $add_lines + $del_lines;
         }
+      } else {
+        // This happens when you add empty files.
+        $changeset->attachHunks(array());
+      }
 
       $changeset->setOldFile($change->getOldPath());
       $changeset->setFilename($change->getCurrentPath());