compositor-rdp: free() can handle NULL pointers

There's no need to check if a pointer exists before passing it to free().
free() can handle NULL pointers.

Signed-off-by: Dawid Gajownik <gajownik@gmail.com>
Reviewed-By: David FORT <contact@hardening-consulting.com>

src/compositor-rdp.c

@@ -1233,11 +1233,8 @@ err_output:
 err_compositor:
 	weston_compositor_shutdown(compositor);
 err_free_strings:
-	if (b->rdp_key)
 	free(b->rdp_key);
-	if (b->server_cert)
 	free(b->server_cert);
-	if (b->server_key)
 	free(b->server_key);
 	free(b);
 	return NULL;