clusterizer: Replace last few seeds instead of discarding new seeds

When the seed list is at capacity, instead of discarding the seeds from
the new meshlet we now replace the last few seeds. This seems to
slightly improve the flow for larger meshes, effectively "compacting"
the list a little at every iteration.

Author: zeux

src/clusterizer.cpp

@@ -837,8 +837,8 @@ size_t meshopt_buildMeshletsFlex(meshopt_Meshlet* meshlets, unsigned int* meshle
 		if (split || (meshlet.vertex_count + best_extra > max_vertices || meshlet.triangle_count >= max_triangles))
 		{
 			seed_count = pruneSeedTriangles(seeds, seed_count, emitted_flags);
-			if (seed_count + kMeshletAddSeeds <= kMeshletMaxSeeds)
-				seed_count += appendSeedTriangles(seeds + seed_count, meshlet, meshlet_vertices, indices, adjacency, triangles, live_triangles, cornerx, cornery, cornerz);
+			seed_count = (seed_count + kMeshletAddSeeds <= kMeshletMaxSeeds) ? seed_count : kMeshletMaxSeeds - kMeshletAddSeeds;
+			seed_count += appendSeedTriangles(seeds + seed_count, meshlet, meshlet_vertices, indices, adjacency, triangles, live_triangles, cornerx, cornery, cornerz);
 
 			unsigned int best_seed = selectSeedTriangle(seeds, seed_count, indices, triangles, live_triangles, cornerx, cornery, cornerz);