For pages without any annotations, applies e.g. to the `tracemonkey.pdf` document, we'll repeatedly try to re-create the `annotationLayer` on every zoom and rotation operation.
The reason that this happens is because we don't insert the `annotationLayer`-div into the DOM unless there's annotations present on the page, which thus means that we miss the existing `annotationLayer`-caching present in the `PDFPageView` implementation.
This is a very old issue, and the easiest solution is to simply always insert an *empty* (and hidden) `annotationLayer`-div such that the existing code/caching starts working for the "no annotations" case as well.
Note that this is consistent with other layers, since e.g. the `textLayer` and/or `annotationEditorLayer` may be empty. Given that only a limited, by default ten, number of pages are ever active at once the additional DOM-elements shouldn't effect things negatively here.
8e56f072e0