net: don't leave hostsPath unrestored on error in TestLookupStaticHost

If the return was reached, then hostsPath would not be properly restored
to its original value. See the (lengthy) discussion at
https://golang.org/cl/15960047/

I assume that this is not for Go 1.2; mailing now since I promised to do so.
I will plan to ping once Go 1.2 is out.

R=rsc, bradfitz
CC=golang-dev
https://golang.org/cl/16200043

src/pkg/net/hosts_test.go

@@ -41,7 +41,7 @@ func TestLookupStaticHost(t *testing.T) {
 		if len(ips) != len(tt.ips) {
 			t.Errorf("# of hosts = %v; want %v",
 				len(ips), len(tt.ips))
-			return
+			continue
 		}
 		for k, v := range ips {
 			if tt.ips[k].String() != v {