Fix AttributeError

[JLipnerPitt]

##Description
Fixed an error (AttributeError: 'str' object has no attribute 'decode') coming from line 792 in images.py when trying to upscale certain images. I'm unsure why certain images didn't need to be decoded.

I changed geninfo = items["comment"].decode('utf8', errors="ignore") on line 792 to

    if isinstance(items["comment"], bytes):
        geninfo = items["comment"].decode('utf8', errors="ignore")
    else:
        geninfo = items["comment"]

This resolved the above error. I reattempted upscaling the directory that originally gave me this error and all the images were successfully upscaled with no further issues. I might have found the reason for this error. I ran some of the images that were causing it through metadata2go.com and noticed they all shared a similar formatted comment:

    b'Paint Tool -SAI- JPEG Encoder v1.00\x00'
    b'File written by Adobe Photoshop\xa8 5.2\x00'

I believe that the original code assumed the metadata would always be in bytes of data, which is then decoded into a string. For whatever reason, some of the images had metadata that was already a string, hence the 'str' object has no attribute 'decode' error. I have no idea what leads to this behavior. I'm assuming it's simply a result of how the metadata is handled originally and what technique is used to encode it. I'm not sure how you can reproduce this on a whim since you won't know this is an issue until you try to upscale an image.

metadata for an image that didn't cause the error:

metadata for an image that caused the error:

Screenshots/videos:

Upscale attempt with original code:

Upscale attempt with new code:

Checklist:

• I have read contributing wiki page
• I have performed a self-review of my own code
• My code follows the style guidelines
• My code passes tests