Fix uninitialized return when no strokes are submitted to a thread

client/speed.js

@@ -43,7 +43,7 @@ async function init_wasm(state) {
         env: { 'memory': memory }
     });
 
-    const nworkers = 1; //navigator.hardwareConcurrency;
+    const nworkers = navigator.hardwareConcurrency;
 
     state.wasm.exports = master_wasm.instance.exports;
     state.wasm.heap_base = state.wasm.exports.alloc_static(0);

client/wasm/lod.c

@@ -207,6 +207,7 @@ do_lod(int *clipped_indices, int clipped_count, float zoom,
 {
     if (clipped_count == 0) {
         result_count[0] = 0;
+        result_batch_count[0] = 0;
         return;
     }