Fix two arc issues

Summary:
  - I caused $parser to be reused in D3732 which I belived was safe, but actually isn't. We end up writing to the same changes. We should make it safe but there's some mess in Phabricator that needs to be cleaned up first.
  - One minor error code thing, variable is undefined.

Test Plan: Ran `arc export --git` on a moved file, got a better result. Ran some command which made me hit the other case and didn't get a fatal anymore.

Reviewers: btrahan, vrana

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D3749

src/parser/ArcanistDiffParser.php

@@ -1158,7 +1158,14 @@ final class ArcanistDiffParser {
       if ($change->getNeedsSyntheticGitHunks()) {
         $diff = $repository_api->getRawDiffText($path, $moves = false);
 
+        // NOTE: We're reusing the parser and it doesn't reset change state
+        // between parses because there's an oddball SVN workflow in Phabricator
+        // which relies on being able to inject changes.
+        // TODO: Fix this.
+        $this->setChanges(array());
+
         $raw_changes = $this->parseDiff($diff);
+
         foreach ($raw_changes as $raw_change) {
           if ($raw_change->getCurrentPath() == $path) {
             $change->setFileType($raw_change->getFileType());

src/workflow/ArcanistDiffWorkflow.php

@@ -588,6 +588,7 @@ EOTEXT
       try {
         $this->requireCleanWorkingCopy();
       } catch (ArcanistUncommittedChangesException $ex) {
+        $repository_api = $this->getRepositoryAPI();
         if ($repository_api instanceof ArcanistMercurialAPI) {
 
           // Some Mercurial users prefer to use it like SVN, where they don't