C++: Fix null pointer access for invalid code

The code snippet provided in the bug report could not be parsed
properly, thus Bind did not generate all expected symbols/names.

The chunk in onConnectOrDisconnectCall() fixes the crash. The other
chunks address triggered QTC_ASSERTs.

Change-Id: Idf508b91b70659d38e59064d4922600f7b31daf8
Task-number: QTCREATORBUG-14709
Reviewed-by: Marco Bubke <marco.bubke@theqtcompany.com>