Generate task fails if file is not an image

[hachecode]

When using the "regenerate thumbnails" command from shell:
bin/cake proffer generate table

I get an exception, and execution breaks:
Exception: Unsupported image type. GD driver is only able to decode JPG, PNG, GIF or WebP files.

I solved it by checking if file is an image before trying to convert.

[davidyell]

Thanks for letting me know!