Fix an assert() failure that could occur in a join query if the RHS of an IN() operat...

Fix an assert() failure that could occur in a join query if the RHS of an IN() operator is a list containing correlated expressions. This problem was introduced by checkin [e130319317e7611938] which was part of the fix for ticket [787fa716be3a7f650c] - so this commit is part of that ticket's fix too.

FossilOrigin-Name: 778b1224a318d0137c7dab8361128f593506d3677267898119b934b4d66dfe38