The first case is simple, as it's a static overflow. Theoretically,
the compiler would be allowed to just remove the complete function as
dead code. This is an error left from the port from int to qsizetype:
Qt 5.15 there has uint(MaxAllocSize) + 1, so use quint here again,
qint64 is wrong.
In the second case, we _may_ reach alloc == MaxAllocSize. Check that,
if we do, we don't then add 1 to it.
Pick-to: 6.3 6.2
Change-Id: I93044ed6f1b77559642fa1e4e8f313cf59eeeb79
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
b1938e5787