Preserving astrometric calculation

[turtlecatvyne]

I'm assuming this will be a matter of copying metadata over... But with the recent 1.8.9-2 release the astrometric data isn't valid after a file is processed in Graxpert. Simple steps to reproduce:

1. Process a file in WBPP
2. Open master in Graxpert, process as usual, save the XISF
3. Open xisf in PixInsight, try to do something like SPCC.

You won't have a valid astrometric solution and you have to run through ImageSolver again.