[clang] [clang][Sema] Fix crash when diagnosing candidates with parameter packs (PR #93079)

[kadir çetinkaya via cfe-commits]

kadircet wrote:

@shafik thx for the pointers, i didn't know this came up before and even there were attempted fixes. I can verify that both of those are also fixed with this patch.

@knightXun do you plan to proceed with https://github.com/llvm/llvm-project/pull/70280 ? If so I am happy to discard this PR in favor of yours.

https://github.com/llvm/llvm-project/pull/93079