sweepbatcher: cancel spendCtx after processing

Function monitorSpendAndNotify used to cancel the context passed to
RegisterSpendNtfn right after starting the goroutine processing results.
Spend notifications were missed.

Now the context is canceled when the goroutine finishes.

Author: starius

sweepbatcher/sweep_batcher.go

@@ -1129,11 +1129,12 @@ func (b *Batcher) monitorSpendAndNotify(ctx context.Context, sweep *sweep,
 	parentBatchID int32, notifier *SpendNotifier) error {
 
 	spendCtx, cancel := context.WithCancel(ctx)
-	defer cancel()
 
 	// Then we get the total amount that was swept by the batch.
 	totalSwept, err := b.store.TotalSweptAmount(ctx, parentBatchID)
 	if err != nil {
+		cancel()
+
 		return err
 	}
 
@@ -1142,11 +1143,14 @@ func (b *Batcher) monitorSpendAndNotify(ctx context.Context, sweep *sweep,
 		sweep.initiationHeight,
 	)
 	if err != nil {
+		cancel()
+
 		return err
 	}
 
 	b.wg.Add(1)
 	go func() {
+		defer cancel()
 		defer b.wg.Done()
 		infof("Batcher monitoring spend for swap %x",
 			sweep.swapHash[:6])