fix(ngap): add nil guards for remaining 3 NGAP handlers

[donivtech]

Summary

Add post-loop nil checks for mandatory IEs in 3 NGAP handlers that lack
dispatcher-level protection via FetchRanUeContext:

• HandleLocationReportingFailureIndication — guard cause, rANUENGAPID
• HandleRRCInactiveTransitionReport — guard rANUENGAPID
• HandleUplinkUEAssociatedNRPPATransport — guard rANUENGAPID, routingID

Prevents nil pointer panics when a gNB omits mandatory IEs from these messages.

Test plan

• go build ./... — clean
• go vet ./ngap/... — clean
• go test ./ngap/... — passes

Signed-off-by: Vinod Patmanathan vinod.patmanathan@forsway.com

[gab-arrobo]

@donivtech thanks for your contribution. Please rebase your PR

[Copilot]

Pull request overview

Adds defensive nil checks in selected NGAP handlers to prevent nil-pointer panics when gNBs omit mandatory IEs, specifically for handlers that don’t get dispatcher-level UE context protection via FetchRanUeContext.

Changes:

• Add post-loop nil guards in HandleLocationReportingFailureIndication for cause and rANUENGAPID.
• Add post-loop nil guard in HandleRRCInactiveTransitionReport for rANUENGAPID.
• Add post-loop nil guards in HandleUplinkUEAssociatedNRPPATransport for rANUENGAPID and routingID.

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[donivtech]

Thanks for the review @gab-arrobo and Copilot.

Pushed an updated version that addresses all feedback:

• Rebased onto latest main
• Log message consistency: aligned post-loop messages with the in-loop decode checks within each handler (RanUeNgapID is nil, routingID is nil, etc.)
• Added nRPPaPDU nil guard: good catch — it's marked reject criticality and the non-UE-associated variant already rejects missing NRPPaPDU, so the UE-associated variant should too.