Issue Type: Bug

1. Have unused variable in the first line of the file const asdf = 0; (any line tbh, just an example)
2. Create decoration on the same line with the after property specified

const decorationType = vscode.window.createTextEditorDecorationType({
	isWholeLine: true,
});
const decorationOptions: vscode.DecorationOptions = {
	range: new vscode.Range(0, 0, 0, 0),
	renderOptions: {
		after: {
			contentText: 'random',
		},
	},
};
editor.setDecorations(decorationType, [decorationOptions]);

3. Try to drag-n-drop text to that line

If I reference that variable (remove unused status) - then dnd works fine again.

VS Code version: Code - Insiders 1.39.0-insider (55825e9, 2019-09-10T05:25:22.729Z)
OS version: Windows_NT x64 10.0.18362