Fix scanner crashing when the last line contains a comment

sqlparser/lib/src/reader/tokenizer/scanner.dart

@@ -391,7 +391,7 @@ class Scanner {
   /// Scans a line comment after the -- has already been read.
   void _lineComment() {
     final contentBuilder = StringBuffer();
-    while (_peek() != '\n' && !_isAtEnd) {
+    while (!_isAtEnd && _peek() != '\n') {
       contentBuilder.write(_nextChar());
     }
 

sqlparser/test/scanner/comments_test.dart

@@ -32,4 +32,13 @@ void main() {
       ' not terminated',
     ]);
   });
+
+  test('supports -- comments on last line', () {
+    const sql = '-- not much to see';
+
+    final tokens = Scanner(sql).scanTokens();
+    expect(tokens, hasLength(2));
+    expect((tokens[0] as CommentToken).content, ' not much to see');
+    expect(tokens[1].type, TokenType.eof);
+  });
 }