[PATCH] xcb: add a timeout control when reading INCR property

[PATCH] xcb: add a timeout control when reading INCR property

For the first call of QXcbClipboard::clipboardReadProperty()
inside of clipboardReadIncrementalProperty() in getSelection(),
it will get a XCB_NONE reply before the contents arrived via
property change. Then we give a chance to read more.

Manually tested with following setups:
* examples/widgets/mainwindows/application with gvim(gtk3)
* examples/widgets/widgets/imageviewer with GIMP 2.10.18(based on
gtk2) and GIMP 2.99.6(based on gtk3 via flatpak)

Fixes: QTBUG-56595
Pick-to: 5.12 5.15 6.1 6.2
Done-With: JiDe Zhang <zhangjide@uniontech.com>
Change-Id: Ib45f08464d39ad79137b1da99808c89b7dca2d08
Reviewed-by: JiDe Zhang <zhangjide@uniontech.com>
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
Gbp-Pq: Name xcb_add_a_timeout_control_when_reading_INCR_property.diff