After the repr updates, we correctly have native num attrs initialize…

…d to NaN. However, Num.new() seems to be expected to give back zero, so add an explicit new that makes this happen. Means we regress no spectests now after reprapi2.

src/core/Num.pm

@@ -13,6 +13,9 @@ my class Num {
         nqp::p6box_i(nqp::unbox_n(self));
     }
 
+    multi method new() { nqp::p6box_n(0) }
+    multi method new($n as Num) { $n }
+
     multi method perl(Num:D:) {
         my $res = self.Str;
         if $res.index('e').defined {