Blackness at the end of Mai's path in Kanon.

[eglaysher]

There's a sequence in SEEN8511 where rlvm just displays black during the end of Mai's sequence.

Things that are probably true, based on some preliminary logging:

• This isn't a recent regression; went back to late 2012 and still happened.
• The alpha is being set correctly. (Logging GraphicsObject::setAlpha() seems to be setting the correct value.)
• The alpha is being used correctly. (Less sure, but at least the value is making it to Texture::renderToScreenAsObject() correctly.)
• The object is being placed correctly. (By the logging triggered by F12).