Cull zero homogeneous vertex positions before rasterization

Fix Playroom top right artifact on Nvidia by clipping zero-position vertices.

src/graphics/shader/recompiler/backend/spirv/spirvEmitterInternal.h

@@ -116,6 +116,7 @@ struct EmitterState {
 	uint32_t                   per_vertex_variable                   = 0;
 	uint32_t                   point_size_variable                   = 0;
 	uint32_t                   clip_distance_variable                = 0;
+	uint32_t                   invalid_position_clip_distance        = UINT32_MAX;
 	uint32_t                   cull_distance_variable                = 0;
 	uint32_t                   layer_variable                        = 0;
 	uint32_t                   viewport_index_variable               = 0;