Inherit information from previous PlaceObject tags

If a PlaceObject tag is missing information (e.g. transformation matrix or colorTransform) then this information needs to be referenced from previous PlaceObject tags. This happens when a new character is placed, but retains the previous transformations, such as when a transformation is applied to a Graphic symbol with different symbols on consecutive frames.

I've had a go at fixing this myself, but feel like someone who knows more about the specifics of the implementation might be better placed now that I've found what the issue is. I can provide an example if prodded.