PROBPLUGIN: ProB Animate Menu for Shared Event Composed Machine

The ProB “Animate” and “Export to Classical B” menu commands are available for Shared Event Composed machines.
However, neither command works for those files.
The Animate command throws an exception on the Console, but no feedback is given to the user.
(The “Export to classical B" command returns an error message to the user.)

Probably we should simply disable those commands for these types of files.

> java.lang.NullPointerException
> at de.prob.ui.eventb.StartAnimationHandler.checkErrorMarkers(StartAnimationHandler.java:114)
> at de.prob.ui.eventb.StartAnimationHandler.execute(StartAnimationHandler.java:77)
> at org.eclipse.ui.internal.handlers.HandlerProxy.execute(HandlerProxy.java:293)
> at org.eclipse.core.commands.Command.executeWithChecks(Command.java:476)
> at org.eclipse.core.commands.ParameterizedCommand.executeWithChecks(ParameterizedCommand.java:508)
> at org.eclipse.ui.internal.handlers.HandlerService.executeCommand(HandlerService.java:169)
> at org.eclipse.ui.internal.handlers.SlaveHandlerService.executeCommand(SlaveHandlerService.java:241)
> at org.eclipse.ui.internal.handlers.SlaveHandlerService.executeCommand(SlaveHandlerService.java:241)
> at org.eclipse.ui.menus.CommandContributionItem.handleWidgetSelection(CommandContributionItem.java:829)
> at org.eclipse.ui.menus.CommandContributionItem.access$19(CommandContributionItem.java:815)
> at org.eclipse.ui.menus.CommandContributionItem$5.handleEvent(CommandContributionItem.java:805)
> at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
> at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4128)
> at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1457)
> at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1480)
> at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1465)
> at org.eclipse.swt.widgets.Widget.notifyListeners(Widget.java:1270)
> at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:3974)
> at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3613)
> at org.eclipse.ui.internal.Workbench.runEventLoop(Workbench.java:2701)
> at org.eclipse.ui.internal.Workbench.runUI(Workbench.java:2665)
> at org.eclipse.ui.internal.Workbench.access$4(Workbench.java:2499)
> at org.eclipse.ui.internal.Workbench$7.run(Workbench.java:679)
> at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
> at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:668)
> at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:149)
> at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:123)
> at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196)
> at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:110)
> at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:79)
> at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:344)
> at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:179)
> at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
> at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
> at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
> at java.lang.reflect.Method.invoke(Method.java:597)
> at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:622)
> at org.eclipse.equinox.launcher.Main.basicRun(Main.java:577)
> at org.eclipse.equinox.launcher.Main.run(Main.java:1410)
>