Fix Invalid Palette Pointer error.

Remove old (and now incorrect) error checking code.
We will now rely on Memory::CopyFromEmu to do bounds checking.

Some games actually load palettes from 0x00000000, despite the fact no valid palette data should ever be there.

This fixes [Issue 7792.](http://code.google.com/p/dolphin-emu/issues/detail?id=7792)