devel/qt6-base: Address CVE-2023-51714

A potential integer overflow has been discovered in Qt's HTTP2
implementation. If the HTTP2 implementation receives more then 4GiB
in total headers, or more than 2GiB for any given header pair, then
the internal buffers may overflow.

Reported by:	vvd via #freebsd-desktop
MFH:		2024Q1
Security:	e2f981f1-ad9e-11ee-8b55-4ccc6adda413

(cherry picked from commit dff10118)