fix crash

quic/core/http/quic_spdy_client_session_base.cc

diff --git a/quic/core/http/quic_spdy_client_session_base.cc b/quic/core/http/quic_spdy_client_session_base.cc
index 93f6880..6709c47 100644
--- a/quic/core/http/quic_spdy_client_session_base.cc
+++ b/quic/core/http/quic_spdy_client_session_base.cc
@@ -183,7 +183,9 @@
   // Since promised_by_id_ contains the unique_ptr, this will destroy
   // promised.
   promised_by_id_.erase(promised->id());
-  headers_stream()->MaybeReleaseSequencerBuffer();
+  if (!VersionUsesQpack(connection()->transport_version())) {
+    headers_stream()->MaybeReleaseSequencerBuffer();
+  }
 }
 
 void QuicSpdyClientSessionBase::OnPushStreamTimedOut(QuicStreamId stream_id) {}
@@ -200,7 +202,9 @@
 void QuicSpdyClientSessionBase::CloseStreamInner(QuicStreamId stream_id,
                                                  bool locally_reset) {
   QuicSpdySession::CloseStreamInner(stream_id, locally_reset);
-  headers_stream()->MaybeReleaseSequencerBuffer();
+  if (!VersionUsesQpack(connection()->transport_version())) {
+    headers_stream()->MaybeReleaseSequencerBuffer();
+  }
 }
 
 bool QuicSpdyClientSessionBase::ShouldReleaseHeadersStreamSequencerBuffer() {