fix disappearing markers

fixes #368

app/src/main/java/net/vonforst/evmap/fragment/MapFragment.kt

@@ -1608,6 +1608,10 @@ class MapFragment : Fragment(), OnMapReadyCallback, MenuProvider {
         mapFragment = null
         _binding = null
         vm.mapProjection = null
+        markers.clear()
+        clusterMarkers = emptyList()
+        searchResultMarker = null
+        searchResultIcon = null
         /* if we don't dismiss the popup menu, it will be recreated in some cases
         (split-screen mode) and then have references to a destroyed fragment. */
         popupMenu?.dismiss()