core/txpool: fix pendingset empty-check

Author: holiman

core/txpool/pending.go

@@ -137,7 +137,7 @@ func (ps *pendingSet) Clear() {
 }
 
 func (ps *pendingSet) Empty() bool {
-	return len(ps.Heads) != 0
+	return len(ps.Heads) == 0
 }
 
 // Pop removes the best transaction, *not* replacing it with the next one from

core/txpool/pending_test.go

@@ -73,6 +73,9 @@ func TestPendingSortAndShift(t *testing.T) {
 		haveCount     = 0
 		prevFee       = uint64(math.MaxInt64)
 	)
+	if txset.Empty() {
+		t.Fatalf("expected non-empty")
+	}
 	for {
 		ltx, fee := txset.Peek()
 		if ltx == nil {