Fix smushing of multiple values in Projects "Additional Hashtags" field

Summary: Ref T10168. When we render this control, we currently don't put commas into the value correctly if there are multiple alternative hashtags.

Test Plan: Edited a project with multiple alternate hashtags. Before change: they all got smushed together. After change: properly comma-separated.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10168

Differential Revision: https://secure.phabricator.com/D15045

src/applications/transactions/editfield/PhabricatorStringListEditField.php

@@ -7,6 +7,11 @@ final class PhabricatorStringListEditField
     return new AphrontFormTextControl();
   }
 
+  protected function getValueForControl() {
+    $value = $this->getValue();
+    return implode(', ', $value);
+  }
+
   protected function newConduitParameterType() {
     return new ConduitStringListParameterType();
   }