fix(pkg/chartutil): Fix test, improve message

Fix inverted equaility check and update error message.

pkg/chartutil/values_test.go

@@ -447,8 +447,8 @@ chapter:
 	if _, err := d.PathValue("chapter.doesntexist.one"); err == nil {
 		t.Errorf("Non-existent key in middle of path should return error: %s\n%v", err, d)
 	}
-	if _, err := d.PathValue(""); err != nil {
-		t.Errorf("Empty path should return error: \n%v", d)
+	if _, err := d.PathValue(""); err == nil {
+		t.Error("Asking for the value from an empty path should yield an error")
 	}
 	if v, err := d.PathValue("title"); err == nil {
 		if v != "Moby Dick" {