fix: don't send empty data

src/file.worker.js

@@ -42,10 +42,13 @@ const throttledPM = (() => {
     }
 
     if (lastUpdate + updateDelay <= now || finish) {
-      pm(limitData(dataCache.join('\n')));
+      const data = limitData(dataCache.join('\n'));
+      if (data) {
+        pm(data);
         lastUpdate = now;
         dataCache = [];
       }
+    }
 
     if (tryAgain) {
       const nextTick = fn => setTimeout(fn, 0);