Fix async upgrade inside cork

src/AsyncSocket.h

@@ -135,6 +135,11 @@ protected:
         getLoopData()->corkedSocket = this;
     }
 
+    /* Returns the corked socket or nullptr */
+    void *corkedSocket() {
+        return getLoopData()->corkedSocket;
+    }
+
     /* Returns wheter we are corked or not */
     bool isCorked() {
         return getLoopData()->corkedSocket == this;