HTML embedded images. #2247
Description
Problem description
nbconvert fails to export to HTML when an image file contains a space (fails with .jpeg and .png, but confirmed fix with .jpeg only).
Version Info
nbconvert 7.16.6
How to reproduce
take a functioning image attachment such as: 
then rename file with a space and embed again: 
Workaround
Ensure image files do not have spaces, as nbconvert seems to remove spaces from filenames when parsing the file and then can't locate the filename after removing spaces.
Also, please don't come at me about putting spaces in file names. Many built-in screenshot utilities produce filenames with spaces.