Don't call tor_tls_set_logged_address till after checking conn->tls

Fixes bug 4531; partial backport of e27a26d5.

changes/bug4531

@@ -0,0 +1,4 @@
+  o Major bugfixes:
+    - Fix null-pointer access that could occur if TLS allocation failed.
+      Fixes bug 4531; bugfix on 0.2.0.20-rc. Found by "troll_un".
+

src/or/connection_or.c

@@ -871,12 +871,12 @@ connection_tls_start_handshake(or_connection_t *conn, int receiving)
 {
   conn->_base.state = OR_CONN_STATE_TLS_HANDSHAKING;
   conn->tls = tor_tls_new(conn->_base.s, receiving);
-  tor_tls_set_logged_address(conn->tls, // XXX client and relay?
-      escaped_safe_str(conn->_base.address));
   if (!conn->tls) {
     log_warn(LD_BUG,"tor_tls_new failed. Closing.");
     return -1;
   }
+  tor_tls_set_logged_address(conn->tls, // XXX client and relay?
+      escaped_safe_str(conn->_base.address));
   connection_start_reading(TO_CONN(conn));
   log_debug(LD_HANDSHAKE,"starting TLS handshake on fd %d", conn->_base.s);
   note_crypto_pk_op(receiving ? TLS_HANDSHAKE_S : TLS_HANDSHAKE_C);