[sqlite] Access Violation in fts5_expr()

[Ralf Junker]

This SQL

   SELECT fts5_expr();

results in an AV here:

   https://sqlite.org/src/artifact/56dcbcbdc9029dd7?ln=145

Reason is that fts5ExprFunction() does not check for at least one 
argument to fts5_expr() here:

   http://sqlite.org/src/artifact/56dcbcbdc9029dd7?ln=1886

Ralf