*This is a follow-up to PRs 6299 and 6441.*
The patch also adds an option to `PDFThumbnailView`, that disables the canvas-to-image conversion entirely, which might be useful in the context of issue 7026.
This includes an optimization to zero the height and width of existing thumbnail canvases, when they are removed and recreated during rotation of the document. (Credit goes to nnethercote, who initially found this in PR 4920.)