Disallow both lexer and parser to be empty.
Disallow both lexer and parser to be empty.

Signed-off-by: Jean Privat <51f8b1fa9b424745378826727452997ee2a7c3d7@pryen.org>
Signed-off-by: Etienne M. Gagnon <bf06ec0eb40152cd863534753d026b021022c851@j-meg.com>

SableCC/sablecc,SableCC/sablecc,SableCC/sablecc,Herve-M/sablecc,Herve-M/sablecc,Herve-M/sablecc,SableCC/sablecc,SableCC/sablecc,Herve-M/sablecc,Herve-M/sablecc