Optimizer can crash when closing the StarterForm while the update service is still running

[ascheibe]

The exception thrown was:

{"Cannot access a disposed object.\r\nObject name: 'StarterForm'."}   
at System.Windows.Forms.Control.MarshaledInvoke(Control caller, Delegate method, Object[] args, Boolean synchronous)
at System.Windows.Forms.Control.Invoke(Delegate method, Object[] args)
at HeuristicLab.PluginInfrastructure.Starter.StarterForm.UpdateApplicationsList() in C:\dev\trunk\sources\HeuristicLab.PluginInfrastructure\3.3\Starter\StarterForm.cs:line 176
at HeuristicLab.PluginInfrastructure.Starter.StarterForm.<CheckUpdatesAvailableAsync>b__a(Task`1 t) in C:\dev\trunk\sources\HeuristicLab.PluginInfrastructure\3.3\Starter\StarterForm.cs:line 95
at System.Threading.Tasks.Task.Execute()

This happened when i started the Optimizer while closing the StarterForm in the meantime. Seems that the update service was still running and when it finished the service call, it tried to update the StarterForm which was already disposed at the time.

[gkronber]

Related to #1038.