Markers in empty elements can cause unexpected errors

[pomek]

The problem occurred for the first time in #7907.

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We agreed that the bug can be hooked deeper, in the engine. However, the PR fixes the bug and the editor does not crash anymore.

As for now, we're fine with that. But in the future, the bug can occur once again and if we will be fixing that, we should revert changes introduced in the PR.

ckeditor5/packages/ckeditor5-link/src/linkui.js

Lines 664 to 687 in eb92cfb

	model.change( writer => {
	const range = model.document.selection.getFirstRange();
	if ( model.markers.has( VISUAL_SELECTION_MARKER_NAME ) ) {
	writer.updateMarker( VISUAL_SELECTION_MARKER_NAME, { range } );
	} else {
	if ( range.start.isAtEnd ) {
	const focus = model.document.selection.focus;
	const nextValidRange = getNextValidRange( range, focus, writer );
	writer.addMarker( VISUAL_SELECTION_MARKER_NAME, {
	usingOperation: false,
	affectsData: false,
	range: nextValidRange
	} );
	} else {
	writer.addMarker( VISUAL_SELECTION_MARKER_NAME, {
	usingOperation: false,
	affectsData: false,
	range
	} );
	}
	}
	} );

Originally posted by @pomek in #8074 (comment)