qtest: do not return freed argument vector from qtest_rsp

qtest: do not return freed argument vector from qtest_rsp

If expected_args is 0, qtest frees the argument vector and then returns it
nevertheless.  Coverity complains; in practice this is not an issue because
expected_args == 0 means that the caller is not interested in the argument
vector, but it would be a potential problem if somebody wanted to add
commands with optional arguments to qtest.

Suggested-by: Kamil Dudka <kdudka@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20201120073149.99079-1-pbonzini@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>