fix deadlock: do not lock Viewport while calling MapAnimator

"GLThread 4500" prio=5 tid=11 MONITOR
at org.oscim.map.MapAnimator.updateAnimation(MapAnimator.java:~186)
  - waiting to lock <0x42105030> (a org.oscim.map.MapAnimator) held by tid=1 (main)

"main" prio=5 tid=1 MONITOR
    at org.oscim.map.Viewport.getMapPosition(Viewport.java:~111)
  - waiting to lock <0x42103368> (a org.oscim.map.Viewport) held by tid=11 (GLThread 4500)
  at org.oscim.map.MapAnimator.animateFling(MapAnimator.java:151)