ENYO-312: Guard against non-existent branding image control.

### Issue
`moon.Panels` patterns that are not `activity` and not `alwaysviewing` were not creating the `branding` control, which was being accessed in `indexChanged` and `brandingSrcChanged`.

### Fix
We add some guard code when accessing the `branding` control.

Enyo-DCO-1.1-Signed-off-by: Aaron Tam <aaron.tam@lge.com>