Fix(jsonrpc): Do not error on missign webxdc info

[Septias]

When an invalid webxdc is set as draft, json-rpc's get_draft fails, because get_webxdc_info which it calls, fails because the zip reader can not read a non-zip file. With this change, any error occurring in get_webxdc_info is ignored and the None-variant is returned instead. I also added a test, that setting invalid xdcs is draft is fine core-wise and checked that the input field stays responsive when a fake.xdc produced like in #6826 is added to draft

close #6826

[link2xt]

If it is a bugfix for the main branch, it's better to base it on main branch and not pgp-contacts branch.

[Septias]

I thought at some point @Hocuri noted that it would reduce merge problems if we just keep this as temporary main branch. I'm not up to date about the current situation on core though.

[Hocuri]

This was an idea of mine, but it's up to @link2xt to decide since he's the one who maintains the PGP-branch, and @link2xt said that he's fine with just maintaining it while we continue merging bug fixes into main. I guess features that interact with PGP-contacts should be implemented on top of PGP-contacts, but also here, if in doubt let's just ask @link2xt beforehand.

[link2xt]

I merge the main branch into pgp-contacts branch from time to time, it's not a problem. This way we can also release bugfixes before we merge pgp-contacts branch into main. I want to squash-merged PGP-branch eventually, so it should have only PGP-contacts related changes compared to main.