Fix typo in FALLBACK_ICON URL

[sultanofcardio]

Explanation of the changes, problem that they are intended to fix.

This PR fixes a typo in FALLBACK_ICON URL. The URL points to the dizquetv PNG icon, but there's a typo in vexorian. It's the first thing I noticed when I opened the web UI, so I thought I'd fix it.

All Submissions:

• [x] I have read the code of conduct.
• [x] I am submitting to the correct base branch

Changes that modify the db structure

• [x] Backwards compatibility: Users running the new code using an existing .disquetv folder will not lose their channels / settings.
• [x] I've implemented the necessary db migration steps if any.

New features

• [x] I understand that the feature may not be accepted if it doesn't fit the upstream app's planned design direction. But that in this case I am encouraged to share this as an available modification other users can use if they want.