Fix memory leak.

The buffer to hold the demangled name is allocated before the
name is demangled. If the parse fails, this buffer is not
deallocated, leaking it. Only create the buffer when the parse
passes.

Test: Ran address sanitizer on host and verified this leaks without
Test: the fix and does not with the fix.
Change-Id: I3ee20727972fc511f63aae2b50f5a34f0c792a5f