Do no reset bounded before incremental sort rescan

ExecReScanIncrementalSort was resetting bounded=false, which means the
optimization would be disabled on all rescans. This happens because
ExecSetTupleBound is called before the rescan, not after it.

Author: James Coleman
Reviewed-by: Tomas Vondra
Discussion: https://postgr.es/m/20200414065336.GI1492@paquier.xyz

src/backend/executor/nodeIncrementalSort.c

@@ -1142,7 +1142,6 @@ ExecReScanIncrementalSort(IncrementalSortState *node)
 	if (node->transfer_tuple != NULL)
 		ExecClearTuple(node->transfer_tuple);
 
-	node->bounded = false;
 	node->outerNodeDone = false;
 	node->n_fullsort_remaining = 0;
 	node->bound_Done = 0;