onedrive: fix folder navigation back to the root folder

Sources/VLCOneDriveTableViewController.m

@@ -87,7 +87,10 @@
 - (IBAction)goBack:(id)sender
 {
     if (_oneDriveController.rootFolder != _oneDriveController.currentFolder) {
-        _oneDriveController.currentFolder = _oneDriveController.currentFolder.parent;
+        if ([_oneDriveController.rootFolder.name isEqualToString:_oneDriveController.currentFolder.parent.name])
+            _oneDriveController.currentFolder = nil;
+        else
+            _oneDriveController.currentFolder = _oneDriveController.currentFolder.parent;
         [_activityIndicator startAnimating];
         [_oneDriveController loadCurrentFolder];
     } else