row_undo_ins_remove_clust_rec(): When rolling back the insert
of a metadata record, also reset the root page state within the
same mini-transaction.

dict_table_t::rollback_instant(): Do not allow index->n_core_fields
to be larger than index->n_fields. This logic exists in the 10.3
branch but was incorrectly removed as part of MDEV-15562 in 10.4.0.