fix comment that got split in two

src/librustc_const_eval/_match.rs

@@ -361,14 +361,13 @@ impl<'tcx> Witness<'tcx> {
 
 /// This determines the set of all possible constructors of a pattern matching
 /// values of type `left_ty`. For vectors, this would normally be an infinite set
+/// but is instead bounded by the maximum fixed length of slice patterns in
+/// the column of patterns being analyzed.
 ///
 /// This intentionally does not list ConstantValue specializations for
 /// non-booleans, because we currently assume that there is always a
 /// "non-standard constant" that matches. See issue #12483.
 ///
-/// but is instead bounded by the maximum fixed length of slice patterns in
-/// the column of patterns being analyzed.
-///
 /// We make sure to omit constructors that are statically impossible. eg for
 /// Option<!> we do not include Some(_) in the returned list of constructors.
 fn all_constructors<'a, 'tcx: 'a>(cx: &mut MatchCheckCtxt<'a, 'tcx>,