ESI VDP to veto being pushed

So far, we relied upon esi not being added to resp_filters for no esi
object, but as the filters can be set freely from VCL, the esi vdp
itself should veto being pushed if it has not business to do with the
object at hand.

bin/varnishd/cache/cache_esi_deliver.c

@@ -259,8 +259,13 @@ ved_vdp_esi_init(struct req *req, void **priv)
 {
 	struct ecx *ecx;
 
+	CHECK_OBJ_NOTNULL(req, REQ_MAGIC);
 	AN(priv);
 	AZ(*priv);
+
+	if (!ObjHasAttr(req->wrk, req->objcore, OA_ESIDATA))
+		return (1);
+
 	ALLOC_OBJ(ecx, ECX_MAGIC);
 	AN(ecx);
 	assert(sizeof gzip_hdr == 10);