ChunkStore: fix row-id computation when removing dangling static chunks

[teh-cmc]

The assertion was correct 🥳🎈.

There was a real memleak in there when dealing with partially dangling static chunks (simplifying a bit: those are static chunks being overwritten for some components but not all, which is a very niche use case, thus why we've never hit it until now).

• Fixes Panic due to assertion chunk_id_removed.is_some() #7992

cc @grtlr

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[abey79]

Looks legit to my uneducated eyes. Did you have a (simple) repro that could be turned into a test? (If not I guess the debug_assert will do).

[teh-cmc]

Did you have a (simple) repro that could be turned into a test? (If not I guess the debug_assert will do).

I do have a simple repro (see original issue), but the bug itself felt too niche and too localized to meet my standards for "worth the maintenance cost of one more test". I'll try and implement and see how bad it is though, just in case.

[teh-cmc]

Ok no it definitely gets over the threshold 😬

[grtlr]

@teh-cmc Thank you for the quick fix! The problems seem to be solved by this.