C++: fixed potential crash for out of bounds access of token_names.

C++: fixed potential crash for out of bounds access of token_names.

Cause: Q_PRIVATE_PROPERTY didn't have an entry in token_names, so if
Token::spell or Token::name was called on a T_Q_GADGET, an out-of-bounds
access would occur.

Change-Id: I1ec7b91a5d3def5508e21ad4f1863a52cb4ed540
Reviewed-on: http://codereview.qt.nokia.com/4207
Reviewed-by: Christian Kamm <christian.d.kamm@nokia.com>