message: Fix uninitialized variable use discovered by MSAN.
diff: @@ -265,7 +265,7 @@ public:
  MockStream stream_;
  Http::StreamCallbacks* stream_callbacks_{nullptr};
  NiceMock<Upstream::MockClusterManager> cluster_manager_;
  - uint32_t initial_buffer_limit_;
  + uint32_t initial_buffer_limit_{};
  bool streaming_filter_{false};
  // TODO(mattklein123): Not all tests have been converted over to better setup. Convert the rest.
  