Fix NPE

[smoser]

10:07:00,287 SEVERE [org.zkoss] (Thread-119) >>java.lang.NullPointerException?

at ch.netzschmiede.flarmradar.web.radar.util.MapUtil?.getRoundedTrackFor(MapUtil?.java:79)
at ch.netzschmiede.flarmradar.web.radar.util.MapUtil?.getIconPathFor(MapUtil?.java:69)
at ch.netzschmiede.flarmradar.web.radar.renderer.MapPlaneRenderer?.newMapitem(MapPlaneRenderer?.java:55)
at org.zkoss.gmaps.Gmaps.onMapDataChange(Gmaps.java:909)
at org.zkoss.gmaps.Gmaps.syncModel(Gmaps.java:836)
at org.zkoss.gmaps.Gmaps.setModel(Gmaps.java:798)
at ch.netzschmiede.flarmradar.web.radar.component.RadarMapPanel?.setPlanePos(RadarMapPanel?.java:199)
at ch.netzschmiede.flarmradar.web.radar.controller.RadarController?.updateRadarMap(RadarController?.java:174)
at ch.netzschmiede.flarmradar.web.radar.controller.RadarController?.onUpdateRadarWindow(RadarController?.java:147)
at sun.reflect.GeneratedMethodAccessor97.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl?.invoke(DelegatingMethodAccessorImpl?.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.zkoss.zk.ui.event.GenericEventListener?.onEvent(GenericEventListener?.java:96)
at org.zkoss.zk.ui.AbstractComponent?.onEvent(AbstractComponent?.java:2741)
at org.zkoss.zk.ui.AbstractComponent?.service(AbstractComponent?.java:2712)
at org.zkoss.zk.ui.AbstractComponent?.service(AbstractComponent?.java:2653)
at org.zkoss.zk.ui.impl.EventProcessor?.process(EventProcessor?.java:136)
at org.zkoss.zk.ui.impl.UiEngineImpl?.processEvent(UiEngineImpl?.java:1699)
at org.zkoss.zk.ui.impl.UiEngineImpl?.process(UiEngineImpl?.java:1484)
at org.zkoss.zk.ui.impl.UiEngineImpl?.endUpdate(UiEngineImpl?.java:1103)
at org.zkoss.zkex.ui.comet.CometServerPush?.deactivate(CometServerPush?.java:391)
at org.zkoss.zk.ui.impl.DesktopImpl?.deactivateServerPush(DesktopImpl?.java:1411)
at org.zkoss.zk.ui.Executions.deactivate(Executions.java:980)
at ch.netzschmiede.flarmradar.web.radar.RadarWindowPush?$WorkingThread?.run(RadarWindowPush?.java:117)