Fix re-initialization of existing double field.

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 4ee7734a2f78c91cfce410268e5954ab35fd614d..fc42fc7ecc43c263aef2dd187b5ef21dae588f73 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -4026,6 +4026,7 @@ MaybeObject* JSObject::SetLocalPropertyIgnoreAttributes(
       Representation representation = lookup.representation();
       Representation value_representation =
           value->OptimalRepresentation(value_type);
+      if (value_representation.IsNone()) break;
       if (!value_representation.fits_into(representation)) {
         MaybeObject* maybe_failure = self->GeneralizeFieldRepresentation(
             lookup.GetDescriptorIndex(), value_representation);