Fix an issue with BuildLogs and web UI during builds

Summary:
Ref T9123. After recent changes, viewing a live build log from the web UI throws a CSRF exception.

Check `start` ("this object is an active log"), not `live` ("this log is open somewhere").

Test Plan: Will push / etc.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T9123

Differential Revision: https://secure.phabricator.com/D14185

src/applications/harbormaster/storage/build/HarbormasterBuildLog.php

@@ -20,7 +20,7 @@ final class HarbormasterBuildLog extends HarbormasterDAO
   const ENCODING_TEXT = 'text';
 
   public function __destruct() {
-    if ($this->live) {
+    if ($this->start) {
       $this->finalize($this->start);
     }
   }