Don't attempt range delivery on a synth response

This could happen on a 200 synth object if the client request had a
Range header. The range code path would fail because it requires an
obj which the synth path doesn't have.

Fixes: #1660

bin/varnishd/cache/cache_http1_deliver.c

@@ -358,7 +358,6 @@ V1D_Deliver(struct req *req, struct busyobj *bo)
 void
 V1D_Deliver_Synth(struct req *req)
 {
-	char *r;
 
 	CHECK_OBJ_NOTNULL(req, REQ_MAGIC);
 	AZ(req->obj);
@@ -395,16 +394,6 @@ V1D_Deliver_Synth(struct req *req)
 	req->vdps[0] = v1d_bytes;
 	req->vdp_nxt = 0;
 
-	if (
-	    req->wantbody &&
-	    !(req->res_mode & RES_ESI_CHILD) &&
-	    cache_param->http_range_support &&
-	    http_GetStatus(req->resp) == 200) {
-		http_SetHeader(req->resp, "Accept-Ranges: bytes");
-		if (http_GetHdr(req->http, H_Range, &r))
-			v1d_dorange(req, NULL, r);
-	}
-
 	WRW_Reserve(req->wrk, &req->sp->fd, req->vsl, req->t_prev);
 
 	/*

bin/varnishtest/tests/r01660.vtc

+varnishtest "#1660: range and synth"
+
+server s1 {
+	rxreq
+	txresp
+} -start
+
+varnish v1 -vcl+backend {
+	sub vcl_recv {
+		return (synth(200, "OK"));
+	}
+} -start
+
+client c1 {
+	txreq -hdr "Range: 0-1"
+	rxresp
+	expect resp.status == 200
+} -run