Catch errors when uploading white avatar

[askvortsov1]

Fixes #2714

Changes proposed in this pull request:
Catch errors in color thief; if the error corresponds to the one thrown when completely white avatars are uploaded, silence the error and directly set the avatarColor value.

Reviewers should focus on:
Unfortunately JS doesn't really provide us with a cleaner way to catch only this error. I'm hesitant to check for the contents of the error message since it's quite generic.

Necessity

• Has the problem that is being solved here been clearly explained?
• If applicable, have various options for solving this problem been considered?
• For core PRs, does this need to be in core, or could it be in an extension?
• Are we willing to maintain this for years / potentially forever?

Confirmed

• Frontend changes: tested on a local Flarum installation.
• Backend changes: tests are green (run composer test).
• Core developer confirmed locally this works as intended.
• Tests have been added, or are not appropriate here.

Required changes:

• Related documentation PR: (Remove if irrelevant)
• Related core extension PRs: (Remove if irrelevant)

[clarkwinkelmann]

Not tested, but looks good to me.

I'm not even sure the instanceof check is required. We could silence all errors that result of calling ColorThief.

Or if we wanted to not catch errors that result from user.avatarColor = (if an extension defines a setter function), we could save the color in a variable and then set the user avatar color outside of the try/catch.

[matteocontrini]

(Shouldn't the title contain "catch" instead of "escape"? 🤔)

[dsevillamartin]

We could silence all errors that result of calling ColorThief.

I'd rather not do this. Catching all TypeErrors is already too much, but not much we can do about it (error message changes depending on minification and other things sometimes)

[askvortsov1]

(Shouldn't the title contain "catch" instead of "escape"? thinking)

Nice, uh, catch 🙈

We could silence all errors that result of calling ColorThief.

I'd rather not do this. Catching all TypeErrors is already too much, but not much we can do about it (error message changes depending on minification and other things sometimes)

Are you happy with this implementation then?

[dsevillamartin]

Are you happy with this implementation then?

I don't love it, but I think it's the best we can do without forking color thief.