Drop now unneeded frame size check

The `for`-loop already skips trivial size frames.

distributed/comm/tcp.py

@@ -267,25 +267,24 @@ async def write(self, msg, serializers=None, on_error="message"):
         try:
             # trick to enque all frames for writing beforehand
             for each_frame_nbytes, each_frame in zip(frames_nbytes, frames):
-                if each_frame_nbytes:
-                    each_frame = memoryview(each_frame)
+                each_frame = memoryview(each_frame)
 
-                    # Make sure that `len(data) == data.nbytes`
-                    # See <https://github.com/tornadoweb/tornado/pull/2996>
-                    each_frame = each_frame.cast("B")
+                # Make sure that `len(data) == data.nbytes`
+                # See <https://github.com/tornadoweb/tornado/pull/2996>
+                each_frame = each_frame.cast("B")
 
-                    # Workaround for OpenSSL 1.0.2 (can drop with OpenSSL 1.1.1)
-                    for i, j in sliding_window(
-                        2, range(0, each_frame_nbytes + C_INT_MAX, C_INT_MAX)
-                    ):
-                        chunk = each_frame[i:j]
-                        chunk_nbytes = chunk.nbytes
+                # Workaround for OpenSSL 1.0.2 (can drop with OpenSSL 1.1.1)
+                for i, j in sliding_window(
+                    2, range(0, each_frame_nbytes + C_INT_MAX, C_INT_MAX)
+                ):
+                    chunk = each_frame[i:j]
+                    chunk_nbytes = chunk.nbytes
 
-                        if stream._write_buffer is None:
-                            raise StreamClosedError()
+                    if stream._write_buffer is None:
+                        raise StreamClosedError()
 
-                        stream._write_buffer.append(chunk)
-                        stream._total_write_index += chunk_nbytes
+                    stream._write_buffer.append(chunk)
+                    stream._total_write_index += chunk_nbytes
 
             # start writing frames
             stream.write(b"")