In PR 5552, specifically commit 9f384bbb41, the meaning of `this.annotationLayer` changed in `PDFPageView`. Previously it referred directly to a DOM element, but now it's instead an instance of `AnnotationsLayerBuilder`.
This patch tweaks things so that we won't try to hide a non-existent `annotationLayer` div in `PDFPageView_reset`, and also so that we don't attempt to insert empty (`null`) DOM elements in `PDFPageView_draw`.