prevent replacing torch_randn globally (instead replacing k_diffusion.sampling.torch) and add a setting to disable this all

 Prompt editing only applies to images in first batch of desired batch size when batch count > 1 #535

fix loopback color correction to store color_correction info for initial image and use that instead of extracting from previous image in a loop #481 #541

... instead of removing them altogether.
This makes the prompt editing filenames [old:new:step] easier to read

fixes bug #464, which happens when controls is None, which leads to args_to being None.

Setting empty envars causes the `os.environ.get('ENVAR', "some default")` pattern in launch.py to ignore it's fallback value.

* fix for odd error only in webp files whereby piexif.insert inserts the bytes correctly, but image.save inserts extra "Exif" in the image metadata which results in an error on reading

Fixes an issue where it's still possible to write to arbitrary directories through careful use of \.. or /.. in directory patterns

...and fix the regex to work better

reeeegex