R1:7a86040f8a46

Avoid exception setting project profile image when GD not installed

Summary:
When trying to set a custom project profile image while the PHP GD extension is not installed, use the same logic which already exists in `PhabricatorFilesComposeAvatarBuiltinFile.php` to set the default project image. This stills display an unhelpful error message `This server only supports these image formats: .` but avoids an exception trying to call GD's `imagecreatefromstring()`.

```
EXCEPTION: (Error) Call to undefined…