sanity check also the urls to self

to fail earlier for a bug exposed by this test which surfaces as garbled
URLs.

src/tests/permutations.vtc

@@ -59,7 +59,8 @@ varnish v1 -arg "-a 127.0.0.1:0 -a self=${tmpdir}/v1.sock" -vcl+backend {
                 set req.url = regsub(req.url,
                   "^/(O[GP])[fp]$", "/\1");
             }
-            elsif (local.socket == "self") {
+            elsif (local.socket == "self" &&
+              req.url ~ "^/O?[GP]$") {
                 # OK
             }
             else {