R1:e74c386d5603

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…