[clang] [Clang] Don't assert non-empty packs for FunctionParmPackExprs (PR #107561)

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

This looks reasonable, I want to think on it a little and give others a chance to look at it, plus I want ot make sure we didn't lose test coverage.  Else LGTM.

https://github.com/llvm/llvm-project/pull/107561