fix signal handling in VUT

55995ab0 turned the VSIG_* flags into
counters, and changed the top of the VUT_Main() accordingly.

We need to reflect the change also further down in the tight loop
calling VSLQ_Dispatch().

Fixes #3436

lib/libvarnishapi/vut.c

@@ -454,7 +454,9 @@ VUT_Main(struct VUT *vut)
 
 		do
 			i = VSLQ_Dispatch(vut->vslq, vut_dispatch, vut);
-		while (i == vsl_more && !VSIG_hup && !VSIG_usr1);
+		while (i == vsl_more &&
+		       VSIG_usr1 == vut->last_sigusr1 &&
+		       VSIG_hup == vut->last_sighup);
 
 		if (i == vsl_more)
 			continue;