Fix an issue where RepositoryQuery may fail for viewers who can't use…

… Diffusion

Summary:
See IRC. We don't always reach `loadPage()`, particularly if `canViewerUseQueryApplication()` fails.

Perform initialization steps in `willExecute()` instead.

Trace from IRC:

```
2015/04/02 11:48:32 [error] 26979#0: *48012 FastCGI sent in stderr: "PHP message: [2015-04-02 11:48:32] EXCEPTION: (Exception) You must execute() the query before accessing the identifier map. at [<phabricator>/src/applications/repository/query/PhabricatorRepositoryQuery.php:134]
PHP message:   #0 PhabricatorRepositoryQuery::getIdentifierMap() called at [<phabricator>/src/applications/diffusion/remarkup/DiffusionRepositoryRemarkupRule.php:26]
PHP message:   #1 DiffusionRepositoryRemarkupRule::loadObjects(array) called at [<phabricator>/src/infrastructure/markup/rule/PhabricatorObjectRemarkupRule.php:309]
PHP message:   #2 PhabricatorObjectRemarkupRule::didMarkupText() called at [<phutil>/src/markup/engine/PhutilRemarkupEngine.php:292]
PHP message:   #3 PhutilRemarkupEngine::postprocessText(array) called at [<phabricator>/src/infrastructure/markup/PhabricatorMarkupEngine.php:138]
PHP message:   #4 PhabricatorMarkupEngine::process() called at [<phabricator>/src/infrastructure/markup/PhabricatorMarkupEngine.php:71]
PHP message:   #5 PhabricatorMarkupEngine::renderOneObject(PhabricatorMarkupOneOff, string, PhabricatorUser) called at [<phabricator>/src/infrastructure/customfield/standard/PhabricatorStandardCustomFieldRemarkup.php:47]
PHP message:   #6 PhabricatorStandardCustomFieldRemarkup::renderPropertyViewValue(array) called at [<phabricator>/src/infrastructure/customfield/field/PhabricatorCustomField.php:1191]
PHP message:   #7 PhabricatorCustomField::renderPropertyViewValue(array) called at [<phabricator>/src/infrastructure/customfield/field/PhabricatorCustomFieldList.php:176]
PHP message:   #8 PhabricatorCustomFieldList::appendFieldsToPropertyList(PhabricatorProject, PhabricatorUser, PHUIPropertyListView) called at [<phabricator>/src/applications/project/controller/PhabricatorProjectProfileController.php:220]
PHP message:   #9 PhabricatorProjectProfileController::buildPropertyListView(PhabricatorProject, PhabricatorActionListView) called at [<phabricator>/src/applications/project/controller/PhabricatorProjectPr
```

Test Plan:
  - Used `rX` in remarkup.
  - Used `rX` in search.
  - Browed Diffusion, etc.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D12264

src/applications/repository/query/PhabricatorRepositoryQuery.php

@@ -138,14 +138,14 @@ public function getIdentifierMap() {
     return $this->identifierMap;
   }
 
+  protected function willExecute() {
+    $this->identifierMap = array();
+  }
+
   protected function loadPage() {
     $table = new PhabricatorRepository();
     $conn_r = $table->establishConnection('r');
 
-    if ($this->identifierMap === null) {
-      $this->identifierMap = array();
-    }
-
     $data = queryfx_all(
       $conn_r,
       'SELECT * FROM %T r %Q %Q %Q %Q',