Insufficient error handling when servers don't serve sane data

[WentTheFox]

When dA servers reply with a 500, that causes knock-on effects in the code:

• Server responds with status 500 and a HTML page with error.

• Error is reported at request-utils.js:218: Failed to get message counts SyntaxError: Unexpected token < in JSON at position 0

• Badge displays as NaNn

• Similar in the popup interface.

• A notification is fired as if new messages are there.

Originally posted by @kav2k on March 8th, 2021