Escaped non-breaking space in alt text query arg breaks picker

[dphiffer]

Problem: I was unable to save the image from this toot. After some guess-and-check URL fiddling, I discovered the problem is with a non-breaking space character in the alt text.

HTTP 200 (alt=foo%20bar):
https://mltshp.com/tools/p?url=http%3A//notes.torrez.org/images/categories/television.png&alt=foo%20bar

HTTP 500 (alt=foo%A0bar):
https://mltshp.com/tools/p?url=http%3A//notes.torrez.org/images/categories/television.png&alt=foo%A0bar