Fix resource leak (src/backend/libpq/be-secure-common.c)

Hi,

Per Coverity.

Coverity reported a resource leak at the function
run_ssl_passphrase_command.
7. alloc_fn: Storage is returned from allocation function
wait_result_to_str.["show details"]

8. noescape: Assuming resource wait_result_to_str(pclose_rc) is not freed
or pointed-to as ellipsis argument to errdetail_internal.

CID 1533043: (#1 of 1): Resource leak (RESOURCE_LEAK)
9. leaked_storage: Failing to save or free storage allocated by
wait_result_to_str(pclose_rc) leaks it.

I think that Coverity is right.

Fix by freeing the pointer, like pclose_check (src/common/exec.c) similar
case.

Patch attached.

best regards,