fix(knowledge): avoid panic on empty table raw content

[MackDing]

Problem

• uploading or editing some knowledge-base table content could fail with code=105000005 and panic on index out of range [0] with length 0
• root cause: packInsertData accessed slice.RawContent[0] without validating that RawContent existed and contained a valid table payload

Fix

• guard against empty RawContent
• guard against nil/non-table/empty table payload before dereferencing index 0
• return typed business errors instead of panicking so the caller can fail gracefully
• add focused tests covering empty payload, invalid payload, and valid table rows

Test

• PATH=/home/clawos/work/.local-go/go/bin:$PATH GOPATH=/home/clawos/work/.gopath GOCACHE=/home/clawos/work/.gocache GOMODCACHE=/home/clawos/work/.gomodcache GOPROXY=https://proxy.golang.org,direct GOSUMDB=sum.golang.org GOFLAGS='-buildvcs=false -p=1' /home/clawos/work/.local-go/go/bin/go test -gcflags='all=-N -l' ./domain/knowledge/service -run 'Test(EventHandle|PackInsertData)' -count=1 -v

[CLAassistant]

All committers have signed the CLA.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[MackDing]

Quick follow-up: this PR is ready on my side. If there is a preferred fix direction or any additional test / guard you’d like for the empty-table case, I’m happy to update it quickly. Thanks for reviewing.

[MackDing]

Quick follow-up: this PR appears mergeable from my side; the remaining blocker looks like required maintainer review. Happy to adjust if you prefer a different approach.

[MackDing]

Checking in on this PR. It is still open and appears to be waiting on maintainer review.

I am happy to adjust the scope or add verification details if that would make review easier.