Merged revision(s) 45140-45141, 45147-45149 from trunk:
Qt: another fix for StretchMaskBlt.related to issue #26004
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Qt: do not allow negative client rect.
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Qt: fixed behaviour of clientRect when we are scrollable form. issue #26200
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Qt: paint event should go to the viewport of TQtWindowArea on scrollable form.issue #26207
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Qt: fix for wrong widget passed to painter constructor in SlotPaintBg().related issue #26207
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git-svn-id: http://svn.freepascal.org/svn/lazarus/branches/fixes_1_2@45180 4005530d-fff6-0310-9dd1-cebe43e6787f