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>
diff --git a/src/compositor-rdp.c b/src/compositor-rdp.c
index 4ef0dd1..6eac7f9 100644
--- a/src/compositor-rdp.c
+++ b/src/compositor-rdp.c
@@ -1233,12 +1233,9 @@
 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->rdp_key);
+	free(b->server_cert);
+	free(b->server_key);
 	free(b);
 	return NULL;
 }