Fetch original_year from master releases for Discogs (#1122)

[dbogdanov]

This adds an additional Discogs API call from inside get_album_info() via a very basic fetch method (it only returns year). This may be expanded in the future to fetch other fields from the master release (genres, styles, etc.) if necessary.

Assume that original_year equals to year for releases without a master release. If parsing the original year in the master release fails, the resulting value is kept as None.

I am not sure how to update tests, because the API call is inside get_album_info. The functionality is so basic that possibly it is not necessary (and other API calls aren't tested as well).

[sampsyo]

Looks great! This information will be useful to have.

I notice that we now have some similar-looking exception-handling code for the calls into the Discogs API. (The handlers for DiscogsAPIError and CONNECTION_ERRORS are very similar between the Master and Release fetching code, for example.) Would it make sense to refactor that code so it can be shared between the different resource retrievals?

[dbogdanov]

May be, but it may also complicate the code. The code is similar for candidates(), album_for_id() and get_master_year() methods. The return values, retry method and log messages are different though. If there will be more methods like this than yes.

[sampsyo]

OK, cool. It's only worth pursuing if it can be done in a way that makes the code simpler, not more complex. Other than that, I think all we need is a changelog entry here.

[sampsyo]

Perfect. Thanks again! ✨

[sampsyo]

...and thanks for all your contributions over the last week or two. I’ve invited you as an organization member, so you should now be able to commit directly. Of course, pull requests are always still an option as a way to get code reviews!