matroskademux: Avoid integer-overflow resulting in heap corruption in WavPack header...

matroskademux: Avoid integer-overflow resulting in heap corruption in WavPack header handling code

blocksize + WAVPACK4_HEADER_SIZE might overflow gsize, which then
results in allocating a very small buffer. Into that buffer blocksize
data is memcpy'd later which then causes out of bound writes and can
potentially lead to anything from crashes to remote code execution.

Thanks to Adam Doupe for analyzing and reporting the issue.

CVE: CVE-2022-1920

https://gstreamer.freedesktop.org/security/sa-2022-0004.html

Fixes https://gitlab.freedesktop.org/gstreamer/gstreamer/-/issues/1226

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/2612>