Force typeahead datasource response into expected array format

Ref T4100. Without this, we sometimes get a sparse array from composite sources and the client isn't sure what to do with it.

src/applications/typeahead/controller/PhabricatorTypeaheadModularDatasourceController.php

@@ -238,6 +238,7 @@ final class PhabricatorTypeaheadModularDatasourceController
     }
 
     $content = mpull($results, 'getWireFormat');
+    $content = array_values($content);
 
     if ($request->isAjax()) {
       return id(new AphrontAjaxResponse())->setContent($content);