No exception is raised when a non-telegram error happens while adding a sticker

[zeroone2numeral2]

The exception should be raised so the bot will warn the user about the error, asking him to report it on GitHub.

For some reasons, it looks like this doesn't happen

Relevant code: https://github.com/zeroone2numeral2/sticker-thief/commit/78e1df0cee777dafbe72b0702186a2d405a2cdc7#diff-F89A7CE49CD45881D6591525FD3B9934R197