Fix memory leak of the demangled symbol name

Fix memory leak of the demangled symbol name

compute_and_set_names would only free the name if we did not find the name
in the hashtable, but it needs to always free it.  Solve this by moving the
smart pointer outside the if.

Thanks to PhilippeW for finding this.

gdb/ChangeLog:

2020-01-09  Christian Biesinger  <cbiesinger@google.com>

	* symtab.c (general_symbol_info::compute_and_set_names): Move the
	unique_xmalloc_ptr outside the if to always free the demangled name.

Change-Id: Id7c6b8408432183700ccb5ff634818d6c5a3ac95