[rlox] Handle incomplete expression

rlox/src/lc.rs

@@ -329,7 +329,9 @@ impl<'src> Parser<'src> {
     }
 
     fn _expression(&mut self, chunk: &mut Chunk, min_prec: Precedence) {
-        match self.scanner.next().unwrap() {
+        match self.scanner.next() {
+            None => panic!("Expected further tokens"),
+            Some(token) => match token {
                 Token {
                     ttype: TokenType::Minus,
                     span: _,
@@ -354,6 +356,7 @@ impl<'src> Parser<'src> {
                     assert_eq!(self.scanner.next().unwrap().ttype, TokenType::RightParen)
                 }
                 _ => panic!("Expected '-' or number"),
+            }
         };
 
         while let Some(op) = self.scanner.next_if(|token| {