qt: minor Win32 thumb bar button fixes

See individual commits, self-explanatory.

Request review @chub.

added MRStatus::NotCompliant label

added 2 commits

• 5129160a - qt: use `hasPrev()`/`hasNext()` instead of `count()` in Win32 thumb bar prev/next buttons
• e9d83d13 - qt: disable Win32 thumb bar buttons instead of hiding

Compare with previous version

added MRStatus::Reviewable label and removed MRStatus::NotCompliant label

changed milestone to %4.0

added Component::Interface: Qt label

requested review from @chub

added MRStatus::WaitingForReviewerFeedback label and removed MRStatus::Reviewable label

approved this merge request

added MRStatus::Acceptable label and removed MRStatus::WaitingForReviewerFeedback label

added MRStatus::Accepted label and removed MRStatus::Acceptable label

MR Acceptance result

This MergeRequest has been Accepted! Congratulations.

MR acceptance checks details:

• MR should be considered mergeable by Gitlab
• Last pipeline should be successful
• MergeRequest should have at least one external review and/or vote
• All threads should be resolved, have votes and score > 0
• MergeRequest should have no activity (threads/votes) for (72h/72h)

This message was automatically generated by homer-bot.

added 78 commits

• e9d83d13...da9b147a - 76 commits from branch videolan:master
• 26994740 - qt: use `hasPrev()`/`hasNext()` instead of `count()` in Win32 thumb bar prev/next buttons
• 629d1d64 - qt: disable Win32 thumb bar buttons instead of hiding

Compare with previous version

enabled an automatic merge when all merge checks for 629d1d64 pass

merged