Fix line count in diffs with more hunks per changeset

Summary: This error usually doesn't occur because we have only one hunk per changeset most of the time.

Test Plan:
  $hunk = new ArcanistDiffHunk();
  $hunk->setAddLines(1);
  $hunk->setDelLines(1);

  $change = new ArcanistDiffChange();
  $change->addHunk($hunk);
  $change->addHunk($hunk);

  $diff = DifferentialDiff::newFromRawChanges(array($change));
  var_dump($diff->getLineCount());

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D2878

src/applications/differential/storage/DifferentialDiff.php

@@ -147,8 +147,8 @@ final class DifferentialDiff extends DifferentialDAO {
           $changeset->addUnsavedHunk($dhunk);
           $add_lines += $hunk->getAddLines();
           $del_lines += $hunk->getDelLines();
-          $lines += $add_lines + $del_lines;
         }
+        $lines += $add_lines + $del_lines;
       } else {
         // This happens when you add empty files.
         $changeset->attachHunks(array());