gpush/gpick: accept commits without Change-id on Change refs

when an upstream is rewound, direct-pushed commits without a Change-id
may suddenly show up on Change refs. there is nothing the user can do
about this, so just accept them and expect the consumer code to be able
to deal with this.

Change-Id: I474472aaa0b533920e5133cf7036a82e0c162599
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>