Pattern tiles were drawn with the default render options, so an image
whose pixels cannot be decoded drew nothing inside a pattern fill even
when the render marks undecoded images, as the canvas does. Tiles now
follow the caller's mark_undecoded_images setting, and the tile cache
keys on it.
An opacity mask with such a pattern now treats the mark as part of the
mask, as it does for an undecodable image outside a pattern.