patch 8.2.3090: in rare cases the cursor may be somewhere in a folded line

patch 8.2.3090: in rare cases the cursor may be somewhere in a folded line

Problem:    With concealing enabled and indirectly closing a fold the cursor
            may be somewhere in a folded line.
Solution:   Recompute the cursor position when the cursor line can be
            concealed. (closes #8480)