cpp-httplib: Use-after-free of TLS session in WebSocketClient::shutdown_and_close()

cpp-httplib is a C++ header-only HTTP/HTTPS library. In versions 0.33.0 through 0.50.0, the TLS-enabled WebSocket client frees the TLS session before closing the WebSocket that still uses it, producing a use-after-free. In WebSocketClient::shutdown_and_close the SSL object is freed and the pointer cleared, but the subsequent WebSocket close still sends a close frame through the SSL socket stream, which holds a raw copy of the now-dangling session pointer and reads from and writes to the freed memory. The same freed-then-used ordering is reachable through the client's destructor and its connect path, so ordinary teardown of a secure WebSocket connection triggers the defect. This issue is fixed in version 0.50.1.