[analyzer] Fix Static Analyzer g_memdup false-positive

`g_memdup()` allocates and copies memory, thus we should not assume that
the returned memory region is uninitialized because it might not be the
case.

PS: It would be even better to copy the bindings to mimic the actual
content of the buffer, but this works too.

Fixes #53617

Reviewed By: martong

Differential Revision: https://reviews.llvm.org/D124436