"Uncaught Invariant Violation: Expected to find a valid target." after cancelling a drag into the react sortable tree

I discovered this issue while integrating react-sortable-tree into my app, but was able to easily reproduce with one of the examples in the storybook.

https://codesandbox.io/s/xzoq6xprlz

Drag the "baby rabbit" box to the React Sortable Tree area, move it around so that it registers with the React Sortable Tree, then move the box out of the React Sortable Tree area such that the placeholder turns red, then release the box outside of the React Sortable Tree area.

This will cause the Console to fire with this error.
```

**browser.js:38 Uncaught Invariant Violation: Expected to find a valid target.
at invariant (https://xzoq6xprlz.codesandbox.io/node_modules/invariant/browser.js:38:15)
at DragDropMonitorImpl.canDropOnTarget (https://xzoq6xprlz.codesandbox.io/node_modules/dnd-core/lib/cjs/DragDropMonitorImpl.js:67:9)**
at DropTargetMonitorImpl.canDrop (https://xzoq6xprlz.codesandbox.io/node_modules/react-dnd/lib/cjs/DropTargetMonitorImpl.js:24:41)
at nodeDropTargetPropInjection (https://xzoq6xprlz.codesandbox.io/node_modules/react-sortable-tree/dist/index.cjs.js:2367:28)
at DragDropContainer.getCurrentState (https://xzoq6xprlz.codesandbox.io/node_modules/react-dnd/lib/cjs/decorateHandler.js:116:29)
at DragDropContainer._this.handleChange (https://xzoq6xprlz.codesandbox.io/node_modules/react-dnd/lib/cjs/decorateHandler.js:45:39)
at handleChange (https://xzoq6xprlz.codesandbox.io/node_modules/dnd-core/lib/cjs/DragDropMonitorImpl.js:27:21)
at dispatch (https://xzoq6xprlz.codesandbox.io/node_modules/redux/lib/redux.js:220:7)
at Object.eval [as endDrag] (https://xzoq6xprlz.codesandbox.io/node_modules/dnd-core/lib/cjs/DragDropManagerImpl.js:67:21)
at HTML5Backend.handleTopDragEndCapture (https://xzoq6xprlz.codesandbox.io/node_modules/react-dnd-html5-backend/lib/cjs/HTML5Backend.js:145:31)
```