update isolate_highest_one for NonZero<T>

Author: vrtgs

library/core/src/num/nonzero.rs

@@ -660,12 +660,15 @@ macro_rules! nonzero_integer {
                         without modifying the original"]
             #[inline(always)]
             pub const fn isolate_highest_one(self) -> Self {
-                let n = self.get() & (((1 as $Int) << (<$Int>::BITS - 1)).wrapping_shr(self.leading_zeros()));
-
                 // SAFETY:
                 // `self` is non-zero, so masking to preserve only the most
                 // significant set bit will result in a non-zero `n`.
-                unsafe { NonZero::new_unchecked(n) }
+                // and self.leading_zeros() is always < $INT::BITS since
+                // at least one of the bits in the number is not zero
+                unsafe {
+                    let bit = (((1 as $Uint) << (<$Uint>::BITS - 1)).unchecked_shr(self.leading_zeros()));
+                    NonZero::new_unchecked(bit as $Int)
+                }
             }
 
             /// Returns `self` with only the least significant bit set.