Disable isDragging when element is destroyed

[nbibler]

While debugging an issue in an application, we came across a case where the act of dragging an element caused re-renders and actively-dragging-element destruction.

In this scenario, ember-sortable would endlessly scroll the page to the top of the screen because the isDragging flag remained true (once dragging began) even after the element was destroyed. This occurred because the _scrollOnEdges method uses requestAnimationFrame to recursively call itself while dragging. If the element is destroyed and isDragging is forever true, these recursive calls will never end.

[jgwhite]

Thank you so much for this submission. I’m really sorry it hasn’t received any attention. I hope to devote the time to reviewing it soon.