Stop animation bug

[samuelobe]

After disconnecting from networking services, the AnimationController runs into the following error:

════════ Exception caught by animation library ═════════════════════════════════
The following StateError was thrown while notifying listeners for AnimationController:
Bad state: Cannot add new events after calling close

When the exception was thrown, this was the stack
#2 MapState.emitMapEvent
package:flutter_map/…/map/map.dart:223
#3 MapState._handleMoveEmit
package:flutter_map/…/map/map.dart:209
#4 MapState.move
package:flutter_map/…/map/map.dart:303
#5 MapControllerImpl.move
package:flutter_map/…/map/map.dart:41
#6 _MapPageState._animatedMapMove.
package:flutter_shuttletracker/…/map_page/map_page.dart:54
...
The AnimationController notifying listeners was: AnimationController#6f6c7(▶ 0.067)
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