[Merkaartor] SEGV when opening geotagged images

[Toby Speight]

I frequently get a segmentation fault when loading JPEG images.  I
traced it down to this code:

/--------
| 		if (positionValid) {
| 			Coord newPos(angToInt(lat), angToInt(lon));
| 			TrackPoint *Pt;
|             QList<MapFeature*>::ConstIterator it = theLayer->get().constBegin();
|             QList<MapFeature*>::ConstIterator end = theLayer->get().constEnd();
| 			for (; it != end; it++) // use existing TrackPoint if there is one in small distance 
| 				if ((Pt = qobject_cast<TrackPoint*>(*it)) &&
| 				 Pt->position().distanceFrom(newPos) <= .002)
| 					break;
| 			if (it == end)
| 				Pt = new TrackPoint(newPos);
| 
| 			Pt->setTag("Picture", "GeoTagged");
| 			usedTrackPoints << TrackPointData(Pt->id(), file, time, it == end);
| 			//if (it == end)
| 				theLayer->add(Pt);
| 				//new AddFeatureCommand(theLayer, Pt, false);
\--------

Looking at the backtrace in gdb, it seems that the
"qobject_cast<TrackPoint*>" sometimes fails, which I think means that
*it isn't a valid QObject.  But I don't know how to investigate further.

For now, my workaround is to disable the iteration, and always create
new points, and that seems to make Merkaartor reliable again for me.