AV in Print Preview when drawing thumbnails

[DanielTr]

Hello,

we we're running into access violations / heap corruptions lately that seem to be caused by GdipDrawImageRectRect when drawing thumbnails.
The access violation didn't occur every time, what makes it not that easy to reproduce. Most of the time it happened when previewing many pages (> 1000).

More information:
TPrintPreview v5.91
TPaperPreview v2.20
TThumbnailPreview v2.11
Delphi XE7
Windows 8.1 and Windows 10

A proposed solution, that seems to work for us, would be to draw the images in TThumbnailPreview.CustomDrawItem only, when the component itself is visible (add "and Self.Visible" to line 5917).

If there are any other suggestions, why this error did occur and how to fix it, we would be happy to be informed.