fix(sbi/consumer): nil-check JsonData on UEContextTransfer 200 response

[SAY-5]

Fixes free5gc/free5gc#1045.

UEContextTransferRequest indexed res.UeContextTransferResponse200.JsonData and immediately dereferenced it for the debug log, but JsonData is *UeContextTransferRspData,omitempty in the OpenAPI model. A source AMF returning a syntactically-valid 200 OK with the jsonData part absent, picked application/json over multipart/related, or sent an empty body, reached here with the pointer nil and the deref panicked the target AMF during cross-AMF UE mobility / 5G-GUTI re-registration.

Guard the deref and surface a clear UeContextTransfer 200 missing JsonData error so the caller can fall through to the foreign-GUAMI handling path instead of crashing.

[SAY-5]

Updated PR title to match Conventional Commits format.

[SAY-5]

Amended commit message to match Conventional Commits format.

[d11nn]

@chchen7 @wiwi878 PTAL

[SAY-5]

Done, trimmed verbose comments and moved context to the PR description. Thanks @roundspring2003!

[SAY-5]

Squashed commits to fix Conventional Commits check.

[roundspring2003]

@SAY-5 plz help to fix the conflict

[SAY-5]

The branch currently shows as mergeable against main with all checks green, so there is no conflict to resolve right now. Let me know if anything else is needed.

[Alonza0314]

Hi @SAY-5 ,

I think it will be better to update the problem detail before the error return after we get in the nil error.

[SAY-5]

Set problemDetails before the missing-JsonData return so callers see a system-failure detail instead of nil (4aeb12b).

[Alonza0314]

Hi @SAY-5 ,
Could you help rebase this to the latest main branch commit? We’ve updated some Go module packages, so rebasing will make it easier for us to run the integration tests.
Thanks!

[d11nn]

@Alonza0314 LGTM, I've rebased this branch to the latest main branch and passed in IT System.