fix rare grass-only chunk meshes

src/graphics/render/BlocksRenderer.cpp

@@ -520,6 +520,13 @@ void BlocksRenderer::build(const Chunk* chunk, const ChunksStorage* chunks) {
     overflow = false;
     vertexOffset = 0;
     indexOffset = indexSize = 0;
+    if (voxelsBuffer->pickBlockId(
+        chunk->x * CHUNK_W, 0, chunk->z * CHUNK_D
+    ) == BLOCK_VOID) {
+        cancelled = true;
+        return;
+    }
+    cancelled = false;
     const voxel* voxels = chunk->voxels;
     render(voxels);
 }

src/graphics/render/BlocksRenderer.hpp

@@ -33,6 +33,7 @@ class BlocksRenderer {
     size_t capacity;
     int voxelBufferPadding = 2;
     bool overflow = false;
+    bool cancelled = false;
     const Chunk* chunk = nullptr;
     std::unique_ptr<VoxelsVolume> voxelsBuffer;
 
@@ -149,4 +150,8 @@ public:
     std::shared_ptr<Mesh> render(const Chunk* chunk, const ChunksStorage* chunks);
     std::shared_ptr<Mesh> createMesh();
     VoxelsVolume* getVoxelsBuffer() const;
+
+    bool isCancelled() const {
+        return cancelled;
+    }
 };

src/graphics/render/ChunksRenderer.cpp

@@ -40,7 +40,9 @@ ChunksRenderer::ChunksRenderer(
         "chunks-render-pool",
         [=](){return std::make_shared<RendererWorker>(level, cache, settings);}, 
         [=](RendererResult& mesh){
-            meshes[mesh.key] = mesh.renderer->createMesh();
+            if (!mesh.renderer->isCancelled()) {
+                meshes[mesh.key] = mesh.renderer->createMesh();
+            }
             inwork.erase(mesh.key);
         }, settings->graphics.chunkMaxRenderers.get())
 {