xcb: add a timeout control when reading INCR property

This is a backport of https://codereview.qt-project.org/c/qt/qtbase/+/306771, it fixes a very annoying bug that prevents pasting big images to Qt apps. E.g. if copy from gimp (release one, based on gtk2) an image that has resolution like 5000x5000 and paste it to a Qt application, it will crash (since gtk2 doesn't handle this X error). When copying from gtk3 applications (like firefox), it just won't paste (at first attempt, at least). This should be reproducible with e.g. neochat.