Fix conditional detecting wasted reconciliation calls

As part of WT-6488 we have added a new conditional to __reconcile that is very complex, and reaches into internal reconciliation data structures used to layout pages (e.g: r->multi_next). We should either move those checks to inside the reconciliation code so we detect the failure earlier, or in the least update the conditional to be more maintainable and not use assumptions about the internal reconciliation structure.