Fix draco extension deserialization

[vb002]

doc.GetObject() returns non const GenericObject which is reseted during GenericValue construction (https://github.com/Tencent/rapidjson/blob/master/include/rapidjson/document.h#L872). It means that such object becomes empty after calling GetMemberValueAsString (as in DeserializeDracoMeshCompression) so you can't use it further. In current master attributes are read after calling GetMemberValueAsString which leads to missing extension params.

[vb002]

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[bghgary]

Ouch, sorry, I just noticed we never responded to this. Is this still needed?

[vb002]

Hi, I think that this problem is still actual.

[bghgary]

Would it be possible for you to add a quick unit test?