Fix missing default value of stream_id and max_data in QuicWindowUpdateFrame.

PiperOrigin-RevId: 384955509

quic/core/frames/quic_window_update_frame.h

diff --git a/quic/core/frames/quic_window_update_frame.h b/quic/core/frames/quic_window_update_frame.h
index e4f2a86..372a4ea 100644
--- a/quic/core/frames/quic_window_update_frame.h
+++ b/quic/core/frames/quic_window_update_frame.h
@@ -31,11 +31,11 @@
 
   // The stream this frame applies to.  0 is a special case meaning the overall
   // connection rather than a specific stream.
-  QuicStreamId stream_id;
+  QuicStreamId stream_id = 0;
 
   // Maximum data allowed in the stream or connection. The receiver of this
   // frame must not send data which would exceedes this restriction.
-  QuicByteCount max_data;
+  QuicByteCount max_data = 0;
 };
 
 }  // namespace quic