avoid panic! in subparsers

src/parser/subparser/collect_till.rs

···
         let mut tokens: Tokens = Tokens::new_empty();
 
         loop {
-            if let Some(_tok) = op.try_next(parser) {
+            if let Some(_token) = op.try_next_token(parser) {
                 break;
             } else {
-                if let Some(tok) = parser.next() {
-                    tokens.add_token(tok);
+                if let Some(token) = parser.next() {
+                    tokens.add_token(token);
                 } else {
                     break;
                 }

src/parser/subparser/collect_while.rs

···
         let mut tokens = Tokens::new_empty();
 
         loop {
-            if let Some(_s) = op.peek_for(parser) {
-                if let Some(tok) = parser.next() {
-                    tokens.add_token(tok)
-                } else {
-                    panic!("Unexpected code path traced");
-                }
+            if let Some(token) = op.try_next_token(parser) {
+                tokens.add_token(token);
             } else {
                 break;
             }