core: don't forget about fallback_smack_process_label

Call setup_smack() also when only fallback_smack_process_label is set.

Fixes: 75689fb2d4

src/core/exec-invoke.c

@@ -4995,7 +4995,7 @@ int exec_invoke(
 #if ENABLE_SMACK
                 /* LSM Smack needs the capability CAP_MAC_ADMIN to change the current execution security context of the
                  * process. This is the latest place before dropping capabilities. Other MAC context are set later. */
-                if (use_smack && context->smack_process_label) {
+                if (use_smack) {
                         r = setup_smack(params, context, executable_fd);
                         if (r < 0 && !context->smack_process_label_ignore) {
                                 *exit_status = EXIT_SMACK_PROCESS_LABEL;