stackFrames primitive sets incorrect filename if phu["ORIGNAME"] does not exists.

[leejjoon]

Here is a relevant code.

DRAGONS/geminidr/core/primitives_stack.py

Line 400 in 32aee56

ad_out.orig_filename = ad_out.phu.get('ORIGNAME')

I understand that ORIGNAME can be set by standardizeHeaders primitive. Still, I think it could be better to simply use 'orig_filename' property of adinputs[0], for example, instead of directly accessing the header.