Use correct FunTyFlag in adjustJoinPointType

As the Lint error in #23952 (closed) showed, the function adjustJoinPointType was failing to adjust the FunTyFlag when adjusting the type.

I don't think this caused the seg-fault reported in the ticket, but it is definitely. This patch fixes it.

It is tricky to come up a small tests case, so this MR does not include one.