day19 working part1, not working part2.

I don't really understand what's expected of part2 and the example is
not simple enough for me to step through in my brain so I'm probably not
going to get it.

src/day19.rs

@@ -48,9 +48,6 @@ impl<'a> Parser<'a> {
                 let mut input = input;
                 let mut iter = a.iter().copied();
                 while let Some(parser_idx) = iter.next() {
-                    if input.is_empty() {
-                        return None;
-                    }
                     input = parsers
                         .get(&parser_idx)
                         .and_then(|p| p.parse(parsers, input))?;