only return offset when different to default

Co-authored-by: Vadim Petrochenkov <vadim.petrochenkov@gmail.com>

Author: richard-uk1

compiler/rustc_lexer/src/lib.rs

@@ -606,7 +606,7 @@ impl Cursor<'_> {
 
     /// Parses a number and in `.1` returns the offset of the literal suffix
     /// (this will be at the end of the token if there is no suffix)
-    fn number(&mut self, first_digit: char) -> (LiteralKind, u32) {
+    fn number(&mut self, first_digit: char) -> (LiteralKind, Option<u32>) {
         debug_assert!('0' <= self.prev() && self.prev() <= '9');
         let mut base = Base::Decimal;
         if first_digit == '0' {