Only add constant folded results to the current SC if they don't have…

… one.

This fixes a bug on JVM where the Attribute type object gets reassigned to the
CORE.setting serialization context (from BOOTSTRAP.nqp), which broke
runtime-creation of Attributes due to an SC-mismatch during Attribute attribute
lookup.

src/Perl6/World.nqp

@@ -2406,7 +2406,7 @@ class Perl6::World is HLL::World {
     # Adds the result of a constant folding operation to the SC and
     # returns a reference to it.
     method add_constant_folded_result($r) {
-        self.add_object($r);
+        self.add_object_if_no_sc($r);
         QAST::WVal.new( :value($r) )
     }