no need to check assertion on fast path.

library/core/src/char/methods.rs

@@ -330,8 +330,6 @@ impl char {
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn to_digit(self, radix: u32) -> Option<u32> {
-        assert!(radix <= 36, "to_digit: radix is too high (maximum 36)");
-
         // the code is split up here to improve execution speed for cases where
         // the `radix` is constant and 10 or smaller
         let val = if radix <= 10 {
@@ -340,6 +338,8 @@ impl char {
                 _ => return None,
             }
         } else {
+            assert!(radix <= 36, "to_digit: radix is too high (maximum 36)");
+
             match self {
                 '0'..='9' => self as u32 - '0' as u32,
                 'a'..='z' => self as u32 - 'a' as u32 + 10,