Reapply "[Concepts] Recover properly from a RecoveryExpr in a concept"

This reverts commit 192d69f7.

This fixes the condition to check whether this is a situation where we
are in a recovery-expr'ed concept a little better, so we don't access an
inactive member of a union, which should make the bots happy.

Differential Revision: https://reviews.llvm.org/D134542