add some debug code for EXT-5394: Crash in LLViewerMediaImpl::calculateInterest()

indra/newview/llviewermedia.cpp

@@ -2875,7 +2875,13 @@ void LLViewerMediaImpl::calculateInterest()
 	if(!mObjectList.empty())
 	{
 		// Just use the first object in the list.  We could go through the list and find the closest object, but this should work well enough.
-		LLVector3d global_delta = gAgent.getPositionGlobal() - (*mObjectList.begin())->getPositionGlobal();
+		std::list< LLVOVolume* >::iterator iter = mObjectList.begin() ;
+		LLVOVolume* objp = *iter ;
+		llassert_always(objp != NULL) ;
+
+		LLVector3d obj_global = objp->getPositionGlobal() ;
+		LLVector3d agent_global = gAgent.getPositionGlobal() ;
+		LLVector3d global_delta = agent_global - obj_global ;
 		mProximityDistance = global_delta.magVecSquared();  // use distance-squared because it's cheaper and sorts the same.
 	}