v.io/x/ref/test: Address a missed code review comment.

This is a small code clenliness issue that I forgot to address.

Change-Id: Ia52eac3ec0e67a36e26a60a834b7f7beb3a4bee6
diff --git a/test/init.go b/test/init.go
index c69aca0..166c68e 100644
--- a/test/init.go
+++ b/test/init.go
@@ -71,7 +71,7 @@
 // Both steps are skipped if this function is invoked from a process run
 // using the modules package.
 func V23Init() (*context.T, v23.Shutdown) {
-	moduleProcess := len(os.Getenv("V23_SHELL_HELPER_PROCESS_ENTRY_POINT")) != 0
+	moduleProcess := os.Getenv("V23_SHELL_HELPER_PROCESS_ENTRY_POINT") != ""
 	return V23InitWithParams(InitParams{
 		CreatePrincipal:  !moduleProcess,
 		CreateMounttable: !moduleProcess,