[3.6] bpo-30594: Fixed refcounting in newPySSLSocket (GH-1992) (#1994)

If pass a server_hostname= that fails IDNA decoding to SSLContext.wrap_socket or SSLContext.wrap_bio, then the SSLContext object had a spurious Py_DECREF called on it, eventually leading to segfaults.
(cherry picked from commit 65ece7c)

Author: njsmith

Modules/_ssl.c

@@ -599,6 +599,7 @@ newPySSLSocket(PySSLContext *sslctx, PySocketSockObject *sock,
     self->ssl = NULL;
     self->Socket = NULL;
     self->ctx = sslctx;
+    Py_INCREF(sslctx);
     self->shutdown_seen_zero = 0;
     self->handshake_done = 0;
     self->owner = NULL;
@@ -613,8 +614,6 @@ newPySSLSocket(PySSLContext *sslctx, PySocketSockObject *sock,
         self->server_hostname = hostname;
     }
 
-    Py_INCREF(sslctx);
-
     /* Make sure the SSL error state is initialized */
     (void) ERR_get_state();
     ERR_clear_error();