Avoid crash when re-saving new contact with photo.

This bug was encountered when creating a new contact from Maps,
but could happen any time you:
- create a new contact
- set a contact photo, either from the gallery or a new photo
- save contact but don't leave ContactEditorFragment
  (eg: "Join" cause the contact to be saved)
- edit another field
- save

The fix is to clear the list of photos-to-save after each save.

Bug: 6432438
Change-Id: I63e86bd82fd16b8177bdca741ecc7a1a90d22d18