Make parameter_index return a Result<Option<_>> instead of squashing string conversion errors into None.
Make parameter_index return a Result<Option<_>> instead of squashing
string conversion errors into None.

gwenn/rusqlite,mikelodder7/rusqlcipher,jgallagher/rusqlite,jgallagher/rusqlite,gwenn/rusqlite,jgallagher/rusqlite,xinghun92/rusqlite,mikelodder7/rusqlcipher,xinghun92/rusqlite,xinghun92/rusqlite,mikelodder7/rusqlcipher,gwenn/rusqlite