Disable speculative Range handling on streaming transactions where

we don't yet know the length.

I attempted to add a way to determine if the object was big enough
*yet* to satisfy the Range, but that was non-viable.

Fixes:	#1777

bin/varnishd/cache/cache_range.c

@@ -137,7 +137,7 @@ vrg_dorange(struct req *req, const char *r)
 		high = req->resp_len - 1;
 	} else if (req->resp_len >= 0 && (high >= req->resp_len || !has_high))
 		high = req->resp_len - 1;
-	else if (!has_high)
+	else if (!has_high || req->resp_len < 0)
 		return (NULL);			// Allow 200 response
 	/*
 	 * else (bo != NULL) {

bin/varnishtest/tests/c00034.vtc

@@ -176,7 +176,7 @@ client c1 {
 		-hdr "Range: bytes=2-5" \
 		-hdr "Accept-encoding: gzip"
 	rxresp
-	expect resp.status == 206
-	expect resp.http.Content-Range == "bytes 2-5/*"
-	expect resp.http.Content-Length == 4
+	expect resp.status == 200
+	gunzip
+	expect resp.bodylen == 100
 } -run

bin/varnishtest/tests/r01777.vtc

+varnishtest "range asked longer than object"
+
+server s1 {
+	rxreq
+	txresp -nolen -hdr "Transfer-Encoding: chunked"
+	delay .5
+	chunkedlen 64
+	chunkedlen 64
+	chunkedlen 0
+} -start
+
+varnish v1 -vcl+backend { } -start
+
+client c1 {
+	txreq -hdr "Range: bytes=0-129"
+	rxresp
+	expect resp.status == 200
+} -run