- Add early check for existing UE context by AMF UE NGAP ID at beginning of rrc_gNB_process_Handover_Request
- Add dedicated function to get UE context by AMF UE NGAP ID: rrc_gNB_get_ue_context_by_amf_ue_ngap_id()
- Send handover failure with appropriate cause if UE context already exists
- Remove redundant ho_context NULL check that could never be true for newly created UE contexts
- Prevents duplicate handover processing and resource leaks