Alpha is ignored on plane masters that are render relay'd

[LemonInTheDark]

If you change the alpha of a plane master which is being render relayed somewhere else using "*" format, the alpha modification is ignored and it continues to render at full opacity.

I'd expect the alpha modification to carry down, but it doesn't.

[LemonInTheDark]

adding a line to plane rendering that mimics how normal textures use alpha seemingly resolves this fine, but it does reintroduce #2548