Reposition crop boundary when window resizes.

public/js/crop_editor.js

@@ -218,6 +218,8 @@ class CropEditor {
 		moveTarget.addEventListener('mousedown', this.moveSelectionStart.bind(this));
 		moveTarget.addEventListener('mousemove', this.moveSelection.bind(this));
 		moveTarget.addEventListener('mouseup', this.moveSelectionEnd.bind(this));
+
+		window.addEventListener('resize', this.positionBoundary.bind(this));
 	}
 
 	cropSelectionStart(event) {