handlers: Handle crash if r.URL.Path is empty. (#3554)

URL paths can be empty and not have preceding separator,
we do not yet know the conditions this can happen inside
Go http server.

This patch is to ensure that we do not crash ourselves
under conditions where r.URL.Path may be empty.

Fixes #3553

cmd/generic-handlers.go

@@ -311,18 +311,7 @@ var notimplementedObjectResourceNames = map[string]bool{
 
 // Resource handler ServeHTTP() wrapper
 func (h resourceHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
-	// Skip the first element which is usually '/' and split the rest.
-	splits := strings.SplitN(r.URL.Path[1:], "/", 2)
-
-	// Save bucketName and objectName extracted from url Path.
-	var bucketName, objectName string
-	if len(splits) == 1 {
-		bucketName = splits[0]
-	}
-	if len(splits) == 2 {
-		bucketName = splits[0]
-		objectName = splits[1]
-	}
+	bucketName, objectName := urlPath2BucketObjectName(r.URL)
 
 	// If bucketName is present and not objectName check for bucket level resource queries.
 	if bucketName != "" && objectName == "" {