Fix overzealous transactions on dashboard panels

Summary: Fixes T10474. This had the same root cause as T10024 -- a missing call to `didSetValueFromStorage()` because of the way the fields work.

Test Plan:
  - Edited a text panel before change, without changing text: got silly transaction.
  - Made change, edited text panel without changing text, no transaction.
  - Made a real edit, got a good transaction.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10474

Differential Revision: https://secure.phabricator.com/D15391

src/applications/dashboard/customfield/PhabricatorDashboardPanelCoreCustomField.php

@@ -21,6 +21,7 @@ final class PhabricatorDashboardPanelCoreCustomField
   public function readValueFromObject(PhabricatorCustomFieldInterface $object) {
     $key = $this->getProxy()->getRawStandardFieldKey();
     $this->setValueFromStorage($object->getProperty($key));
+    $this->didSetValueFromStorage();
   }
 
   public function applyApplicationTransactionInternalEffects(