Test set.matched() with a negative argument.

src/tests/set.vtc

@@ -34,7 +34,7 @@ varnish v1 -vcl {
 
 		set resp.http.unanchored1 = unanchored.match("foobar");
 		set resp.http.unanchored1n = unanchored.nmatches();
-		# set resp.http.unanchored1--1 = unanchored.matched(-1);
+		set resp.http.unanchored1--1 = unanchored.matched(-1);
 		set resp.http.unanchored1-0 = unanchored.matched(0);
 		set resp.http.unanchored1-1 = unanchored.matched(1);
 		set resp.http.unanchored1-2 = unanchored.matched(2);
@@ -104,6 +104,7 @@ client c1 {
 	expect resp.http.unanchored-1-illegal == "false"
 	expect resp.http.unanchored1 == "true"
 	expect resp.http.unanchored1n == "2"
+	expect resp.http.unanchored1--1 == "false"
 	expect resp.http.unanchored1-0 == "false"
 	expect resp.http.unanchored1-1 == "true"
 	expect resp.http.unanchored1-2 == "true"
@@ -142,6 +143,7 @@ logexpect l1 -v v1 -d 1 -g vxid -q "VCL_Error" {
 	expect 0 * Begin req
 	expect * = VCL_Error "^vmod re2 error: unanchored.nmatches.. called without prior match$"
 	expect * = VCL_Error "^vmod re2 error: unanchored.matched.1. called without prior match$"
+	expect * = VCL_Error "^vmod re2 error: n=-1 out of range in unanchored.matched.. .2 patterns.$"
 	expect * = VCL_Error "^vmod re2 error: n=0 out of range in unanchored.matched.. .2 patterns.$"
 	expect * = VCL_Error "^vmod re2 error: n=3 out of range in unanchored.matched.. .2 patterns.$"
 	expect * = End