Fix parsing of ingredients with addendum but no unit

Where an ingredient has no unit (for example, 2 eggs), the parser was
interpreting `{eggs, 2, large}` as "2, large of eggs", instead of as
"2 eggs (large)".

src/lib.rs

@@ -102,6 +102,11 @@ fn capture(chars: &[char]) -> Option<(Ingredient, usize)> {
                 unit = Some(String::new());
                 break;
             }
+            Some(&',') => {
+                i += 1;
+                addendum = Some(String::new());
+                break;
+            }
             Some(&'}') => {
                 i += 1;
                 break;
@@ -115,6 +120,7 @@ fn capture(chars: &[char]) -> Option<(Ingredient, usize)> {
     }
 
     // Unit
+
     if let Some(ref mut unit) = unit {
         loop {
             match chars.get(i) {