fix _SSLContext invalid protocol errors not ensuring a self.ctx, leading to a

potential crash in its destructor
(grafted from c1ddf2d919a18fa4ebec03ce84e1a0457f4396ad)

pypy/module/_ssl/interp_ssl.py

@@ -90,6 +90,8 @@ def ssl_error(space, msg, errno=0):
 
 
 class SSLContext(W_Root):
+    ctx = lltype.nullptr(SSL_CTX.TO)
+
     def __init__(self, space, protocol):
         if protocol == PY_SSL_VERSION_TLS1:
             method = libssl_TLSv1_method()