stream: fixup sync pull batching in stream/new

Author: jasnell

lib/internal/streams/new/pull.js

@@ -285,14 +285,14 @@ function* applyStatelessSyncTransform(source, transform) {
  */
 function* applyStatefulSyncTransform(source, transform) {
   const output = transform(source);
-  const batch = [];
   for (const item of output) {
+    const batch = [];
     for (const chunk of flattenTransformYieldSync(item)) {
       ArrayPrototypePush(batch, chunk);
     }
-  }
-  if (batch.length > 0) {
-    yield batch;
+    if (batch.length > 0) {
+      yield batch;
+    }
   }
 }