RUSTSEC-2024-0357: `MemBio::get_buf` has undefined behavior with empty buffers

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Details
Package	openssl
Version	0.10.44
URL	rust-openssl/rust-openssl#2266
Patched Versions	>=0.10.66
Aliases	GHSA-q445-7m23-qrmw

Previously, MemBio::get_buf called slice::from_raw_parts with a null-pointer, which violates the functions invariants, leading to undefined behavior. In debug builds this would produce an assertion failure. This is now fixed.