Fixed an Unhandled Error in badges.go

There was an unhandled error in badges.go. If you pass an invalid
branch to the badge handler (http://beta.drone.io/github.com/drone/drone/
status.svg?branch=this) the browser is told to redirect to a blank string.
This is unintended behavior. Now, a 404 response is sent instead.

pkg/handler/badges.go

@@ -43,7 +43,11 @@ func Badge(w http.ResponseWriter, r *http.Request) error {
 	// get the latest commit from the database
 	// for the requested branch
 	commit, err := database.GetBranch(repo.ID, branchParam)
-	if err == nil {
+	if err != nil {
+		http.NotFound(w, r)
+		return nil
+	}
+
 	switch {
 	case commit.Status == "Success" && len(successParam) == 0:
 		// if no success image is provided, we serve a
@@ -63,7 +67,6 @@ func Badge(w http.ResponseWriter, r *http.Request) error {
 		// otherwise load unknown image
 		badge = badgeUnknown
 	}
-	}
 
 	http.Redirect(w, r, badge, http.StatusSeeOther)
 	return nil