qRound does not handle overflow

qRound(double d) is documented to "Rounds d to the nearest integer.". If d is outside the range of integers (overflow), it should therefore clamp the result to INT_MAX (or INT_MIN).

Instead, it triggers UB, as it just converts the double to integer (after some adjustements), without checking whether it's in bounds or not. This is https://eel.is/c++draft/conv.fpint#1.sentence-3

This has a cascading effect, for instance the geometry classes use qRound internally, causing for instance a QRectF -> QRect conversion to also trigger UB. There's at least an autotest (tst_QRect::comparison(WithQREAL_MIN)) where this happens.