xcb: only set base size when it's valid
requested to merge asturmlechner/qtbase:asturmlechner/QTBUG-117702-xcb-only-set-base-size-when-valid into kde/5.15
In rare situation, base size could be (-1,-1) or (-2,-2) for high dpi, it will be converted into huge positive numbers.
https://tronche.com/gui/x/icccm/sec-4.html
If a base size is not provided, the minimum size is to be used in its place and vice versa.
Pick-to: 6.6 6.5 6.2 5.15 Task-number: QTBUG-117702 Change-Id: I900ed82f2291fb454d7e34a0dee27459d0a57240 Reviewed-by: Qt CI Bot qt_ci_bot@qt-project.org Reviewed-by: Tor Arne Vestbø tor.arne.vestbo@qt.io Reviewed-by: Axel Spoerl axel.spoerl@qt.io (cherry picked from commit 25720f5a)
Note: Not yet in 5.15 branch, see also: https://bugreports.qt.io/browse/QTBUG-117702