Blender Git Loki

BGE: Fix T35188: Duplicate an instance of group.

This behavior caused a double free.
Before when we duplicated an instance of a group the new instance keep the pointer of the group but was not added in the group instance list (normal).
And during the object deletion we tried to remove the object in the instance list but anyways if it failed decrement the reference count.
Set the group and the instance list to NULL in ProcessReplica avoid these kind of problems.