Call to a member function attachRepository() on a non-object in DiffusionRequest.php

When a new repository is added and daemons haven't finished parsing all commits user can face an exception page  trying to open single commit details page (in example: `/rPH796db9f9c650b6342f0b814ed0f756543de783fd`)
```
>>> UNRECOVERABLE FATAL ERROR <<<

Call to a member function attachRepository() on a non-object

/home/bartek/phabricator/phabricator/src/applications/diffusion/request/DiffusionRequest.php:280


┻━┻ ︵ ¯\_(ツ)_/¯ ︵ ┻━┻
```

I've added checking whether SQL query returned commit data.