- Instead of user name.
- Due to issues with advanced charts like emoji zero-width-joiners.
- Could also have security concerns on untrusted instances with certain
webserver config due to double extension possibilities.
Closes#1993
Thumbnail generation would sometimes create a file larger than the
original, if the original was already well optimized, therefore making
the thumbnail counter-productive. This change compares the sizes of the
original and the generated thumbnail, and uses the smaller of the two if
the thumbnail does not change the aspect ratio of the image.
Fixes#1751
