Use verbatim commit message if it couldn't be parsed

Summary:
We currently remove an invalid user from Reviewers and similar fields and print a note in the template. There are several problems:

# If I only made a typo in the name then it takes some effort to fix this typo and put the name on the original place (this information is lost).
# The notice is almost invisible and most users will just confirm the message without noticing it.
# If I fill the data in the commit message (and not in the template) then I probably want to treat that as authoritative so I want it to be correct.

Test Plan:
`arc diff` with invalid reviewer in commit message.
`arc diff` on empty commit message.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin, nh

Differential Revision: https://secure.phabricator.com/D2730

src/workflow/ArcanistDiffWorkflow.php

@@ -1339,6 +1339,10 @@ EOTEXT
         $template_is_default = true;
       }
 
+      if ($notes) {
+        $commit = head($this->getRepositoryAPI()->getLocalCommitInformation());
+        $template = $commit['message'];
+      } else {
         $template = $conduit->callMethodSynchronous(
           'differential.getcommitmessage',
           array(
@@ -1347,6 +1351,7 @@ EOTEXT
             'fields'      => $fields,
           ));
       }
+    }
 
     if ($included) {
       foreach ($included as $k => $commit) {