added some probably forgotten promise resolutions

[TheBluestBird]

PR check list:

• [x] Document your code
• [x] Add \since QXmpp 1.X, QXMPP_EXPORT
• [x] Fix doxygen warnings (see log when building with -DBUILD_DOCUMENTATION=ON)
• [x] Update doc/doap.xml
• [x] Add unit tests
• [x] Format the code: Run clang-format -i src/<edited-file(s)> tests/<edited-file(s)>

The changes are insignificant, it doesn't feel like it requires to document them or do some meta work. But if you'll tell - I'm gonna try to cover that case in unit testing

[melvo]

Thanks! It was introduced by b17284ee7d674416e0d11f1699f73fcc606262d4. Please write the commit message starting with an upper case letter and the imperative.

[TheBluestBird]

This way will do?

[melvo]

Yes, thanks!