ScalarInt: size mismatches are a bug, do not delay the panic

compiler/rustc_const_eval/src/interpret/validity.rs

@@ -653,8 +653,8 @@ impl<'rt, 'tcx, M: Machine<'tcx>> ValidityVisitor<'rt, 'tcx, M> {
         let WrappingRange { start, end } = valid_range;
         let max_value = size.unsigned_int_max();
         assert!(end <= max_value);
-        let bits = match scalar.try_to_int() {
-            Ok(int) => int.assert_bits(size),
+        let bits = match scalar.try_to_scalar_int() {
+            Ok(int) => int.to_bits(size),
             Err(_) => {
                 // So this is a pointer then, and casting to an int failed.
                 // Can only happen during CTFE.