draft: fix jpeg and exif data handling

[vladmandic]

using jpeg in automatic was somewhat broken when going back-and-forth from txt2img to extras as exif data was overwritten
and switching backt to png meant that pnginfo data was corrupt with previously encoded exif data

• initialize pnginfo if exif data is already present
• generate exif string from pnginfo` so they are always in-sync
• fix infamous KeyError: '.jpg' (not fully fixed in Dirty fix for missing PIL supported file extensions #5838 and tons of bug reports to quote)
• avoid double file write when saving jpeg file

[dathide]

I've been using this for a few hours and haven't encountered any issues. Edit: Thanks for your work on this!

[AUTOMATIC1111]

exif_str += str(v) if k == 'parameters' else f"\n{k}: {v}"

Why is extra stuff added here? Will pnginfo tab be able to read this properly?

[vladmandic]

exif_str += str(v) if k == 'parameters' else f"\n{k}: {v}"

Why is extra stuff added here? Will pnginfo tab be able to read this properly?

previously only latest info passed was used as exif string, so any previous info was simply lost.

for example txt2img worked fine as that is "new info", but then using upscaling from extras would append correct info (as a separate section) in pnginfo, but use only new info from extras to create exif string - previous info was lost.

this simply uses whatever is in pnginfo to create exif string and does not try to create exif string separately.
and yes, png info has no issues with it.

[AUTOMATIC1111]

Here's what I get when I send params from png info to txt2img. The image was generated in txt2img and upscaled in extras tab.

Here's the image.

Also I'm against making this more complicated for PNG info or putting some extended format into JPEG comment. I would prefer if JPEGs stayed as they are.

[vladmandic]

ok, this is an issue and i'll fix it.

i don't think jpeg can stay as-is as its broken - exif gets overwritten with every new operation - its totally unusable
(unlike metadata in png files which is perfect)