Fix folly/io/async/test:async_test - AsyncSSLSocketTest.ConnectTFOFallbackTimeout SIGSEGV

Summary: Fix folly/io/async/test:async_test - AsyncSSLSocketTest.ConnectTFOFallbackTimeout SIGSEGV

Reviewed By: djwatson

Differential Revision: D9520104

fbshipit-source-id: c1133bcb0617ca7f8d5f8a9ee46080c7c7f5b105

folly/io/async/test/TestSSLServer.h

@@ -86,8 +86,10 @@ class SSLServerAcceptCallbackBase : public AsyncServerSocket::AcceptCallback {
   virtual void connAccepted(const std::shared_ptr<AsyncSSLSocket>& s) = 0;
 
   void detach() {
+    if (socket_) {
       socket_->detachEventBase();
     }
+  }
 
   StateEnum state;
   HandshakeCallback* hcb_;