Simplify block gen code path when all corners are empty

src/voxel/world.rs

@@ -39,10 +39,13 @@ impl Chunk {
                 }
             }
 
+            // If all the corners are negative, then all the interpolated values
+            // will be negative too. In that case we can just fill with empty.
+            if block_sign == -8.0 {
+                block.resize(512, Voxel::Empty);
+            } else {
                 let mut vals = [0.0f32; 512];
-            if block_sign != -8.0 {
                 math::tri_lerp_block(&noise_vals, &[8, 8, 8], &mut vals);
-            }
 
                 let mut idx = 0;
                 for z in 0..8 {
@@ -63,6 +66,7 @@ impl Chunk {
                     }
                 }
             }
+        }
 
         block.to_owned()
     }