dnd.js: Fix window freeze on rapid taskbar clicks

[carsteneu]

Fixes #13462

Problem

When users click rapidly on taskbar icons, windows can become unresponsive - clicks inside the window content have no effect until the user clicks on the title bar or maximizes/minimizes the window.

Root Cause

The issue is in js/ui/dnd.js in the _onButtonPress handler. When a button press event occurs, the code calls _grabActor() to grab the pointer for potential drag operations. However, if another click happens before the previous grab is properly released (which can happen during rapid clicking), the grabs accumulate and the pointer gets stuck in a grabbed state.

Solution

Before starting a new grab in _onButtonPress, check if there's already an existing grab (this._onEventId is set) and clean it up first by calling _ungrabActor(). This ensures only one grab is active at a time and prevents the accumulation that causes the freeze.

Changes

• Added cleanup logic in _onButtonPress to release any existing grab before creating a new one
• This is a minimal, targeted fix that doesn't change the overall drag-and-drop behavior

Testing

• Rapid clicking on taskbar icons no longer causes window freezes
• Normal drag-and-drop operations still work correctly
• Window switching via taskbar clicks works as expected