Fix ImportGraphics to not cause sprites to break when it is used

[Grossley]

ImportGraphics has been unstable for a long time, it should be corrected to properly handle sprites, possibly by only allowing padded sprites to be imported.

[Jacky720]

I don't know of any current instability in ImportGraphics (though it does tend to assume all sprites being imported are padded), @Grossley can you clarify?