fixup! doc: remove assignment in condition in stream doc

Author: Trott

doc/api/stream.md

@@ -1033,11 +1033,10 @@ available, [`stream.read()`][stream-read] will return that data.
 const readable = getReadableStreamSomehow();
 readable.on('readable', function() {
   // There is some data to read now.
-  let data = this.read();
+  let data;
 
-  while (data) {
+  while ((data = this.read()) !== null) {
     console.log(data);
-    data = this.read();
   }
 });
 ```