don't overwrite the faked up type details for hv-with-aux

[tonycoz]

Detected by coverity as:

340472 Unused value

An assigned value that is never used may represent unnecessary computation, an incorrect algorithm, or possibly the need for cleanup or refactoring.

In Perl_sv_clear: A value assigned to a variable is never used. (CWE-563)

[nwc10]

Oops. "Thanks applied".

That would have been "leaking" pointers to bodies allocated from arenas, but would never have shown up under any leak checker. With -DPURIFY arenas aren't used, so everything is just malloc/free, and so bodies are passed to free without "thinking too hard" about what the "body details" metadata says to do. Without -DPURIFY bodies would themselves leak, but the arena doesn't leak, so that would be correctly freed at interpreter full destruction, and nothing would have realised.