Crash when replaying tlog file

```
Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
0   com.diydrones.apmplanner2     	0x000000010d67c48d WaypointEditableView::setCurrent(bool) + 29 (WaypointEditableView.cc:635)
1   com.diydrones.apmplanner2     	0x000000010d530e36 WaypointList::currentWaypointEditableChanged(unsigned short) + 230 (WaypointList.cc:393)
2   com.diydrones.apmplanner2     	0x000000010d530e94 WaypointList::currentWaypointViewOnlyChanged(unsigned short) + 36 (WaypointList.cc:408)
3   com.diydrones.apmplanner2     	0x000000010d94eefc WaypointList::qt_static_metacall(QObject*, QMetaObject::Call, int, void**) + 604 (moc_WaypointList.cpp:111)
```

Not sure how this can actually happen... but at least this patch prevents APM from crashing,