GODT-1351: Fix used size update from mail operations

pkg/pmapi/events.go

@@ -45,6 +45,9 @@ type Event struct {
 	Addresses []*EventAddress
 	// Messages to show to the user.
 	Notices []string
+
+	// Update of used user space
+	UsedSpace *int64
 }
 
 // EventAction is the action that created a change.
@@ -184,6 +187,21 @@ func (c *client) getEvent(ctx context.Context, eventID string, numberOfMergedEve
 		return nil, err
 	}
 
+	// API notifies about used space two ways:
+	//    - by `event.User.UsedSpace`
+	//    - by `event.UsedSpace`
+	//
+	// Because event merging is implemented for User object we copy the
+	// value from event.UsedSpace to event.User.UsedSpace and continue with
+	// user.
+	if event.UsedSpace != nil {
+		if event.User == nil {
+			event.User = &User{UsedSpace: event.UsedSpace}
+		} else {
+			event.User.UsedSpace = event.UsedSpace
+		}
+	}
+
 	if event.More && numberOfMergedEvents < maxNumberOfMergedEvents {
 		nextEvent, err := c.getEvent(ctx, event.EventID, numberOfMergedEvents+1)
 		if err != nil {