Do not skip over TK_IF_NULL_ROW operators when bypassing TK_COLLATE operators.

Fix to check-in [ac31edd3eeafcef4] which was itself a fix for ticket
[45f4bf4eb4ffd788].

FossilOrigin-Name: 871f2ddcfbb9196dbd851a350e3471ee6d242d86bbd755201f7e2406fce3ac55