Switch assertion order to be more helpful to ppl that encounter them

Author: oli-obk

src/librustc_mir/const_eval/eval_queries.rs

@@ -124,13 +124,13 @@ pub(super) fn op_to_const<'tcx>(
             ConstValue::ByRef { alloc, offset: ptr.offset }
         }
         Scalar::Raw { data, .. } => {
+            assert!(mplace.layout.is_zst());
             assert_eq!(
                 data,
                 mplace.layout.align.abi.bytes().into(),
                 "this MPlaceTy must come from `try_as_mplace` being used on a zst, so we know what
                  value this integer address must have",
             );
-            assert!(mplace.layout.is_zst());
             ConstValue::Scalar(Scalar::zst())
         }
     };