Assert for untested NV097_SET_VERTEX_DATA2S

[JayFoxRox]

xqemu/hw/xbox/nv2a.c

Line 4430 in 9162957

assert(false); /* FIXME: Untested! */

At the time of writing, this was an assumption and we weren't aware of any games using it.
Now we know of:

• Baldur's Gate: Dark Alliance II
• BMX XXX
• Conker Live and Reloaded
• Halo
• Halo 2
• Kameo Elements of Power
• Steel Battalion: Line of Contact

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A unit test for all of these functions should be written, probably using NXDK-RDT and readback from the GPU to verify how the data was parsed into the vertex