Make "bin/config set --database ..." resurrect deleted values

Summary:
Fixes T12409. Config entries may be marked as "deleted", and `bin/config set --database` doesn't un-delete them, so the edit doesn't do anything.

The "most correct" fix here is to swap to transactions so we run the same code, but just fix this narrowly for now since it's one line of code.

Test Plan:
  - Set `maniphest.default-priority` to `123`.
  - Deleted `maniphest.default-priority` from the web UI by deleting all the text in the box.
  - Before patch: `bin/config set --database maniphest.default-priority 789` had no effect.
  - After patch: `bin/config set --database maniphest.default-priority 789` worked.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T12409

Differential Revision: https://secure.phabricator.com/D17506

src/applications/config/management/PhabricatorConfigManagementSetWorkflow.php

@@ -158,6 +158,10 @@ final class PhabricatorConfigManagementSetWorkflow
       $config_type = 'database';
       $config_entry = PhabricatorConfigEntry::loadConfigEntry($key);
       $config_entry->setValue($value);
+
+      // If the entry has been deleted, resurrect it.
+      $config_entry->setIsDeleted(0);
+
       $config_entry->save();
     } else {
       $config_type = 'local';