fs: Push always a new buffer

fix jerryscript-project#1974

IoT.js-DCO-1.0-Signed-off-by: Lauri Rooden [email protected]

src/js/fs.js

@@ -449,8 +449,7 @@ try {
         // null must be pushed so the 'end' event will be emitted.
         self.push(null);
       } else {
-        self.push(bytes_read == self._buff.length ?
-                  self._buff : self._buff.slice(0, bytes_read));
+        self.push(self._buff.slice(0, bytes_read));
         self.doRead();
       }
     });