Drop superfluous conditionals around g_free()

There is no need to guard g_free(P) with if (P): g_free(NULL) is safe.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20220923090428.93529-1-armbru@redhat.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>