Fix initialization of FDW batching in ExecInitModifyTable
ExecInitModifyTable has to initialize batching for all result relations,
not just the first one. Furthermore, when junk filters were necessary,
the pointer pointed past the mtstate->resultRelInfo array.
Per reports from multiple non-x86 animals (florican, locust, ...).
Discussion: https://postgr.es/m/
20200628151002.7x5laxwpgvkyiu3q@development