Flatpak 2.1.1: Random crash on attempt to switch between tools

[Vitaly Novichkov]

Sometimes I get a crash when selecting the Line/Curve tool. I do switch between rectangle with circular corners and the Line/Curve, and sometimes I get the crash. Also, I may get a crash when opening another file (and closing previous one) without closing the Pinta before.

The system: Linux Mint 21.1 (Ubuntu 22.04)

Now I finally got an error message (before, the Pinta had to just close without any errors):

```
System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation.
 ---> System.IndexOutOfRangeException: Index was outside the bounds of the array.
   at Pinta.Core.ToolManager.DeactivateTool(BaseTool tool, BaseTool newTool)
   at Pinta.Core.ToolManager.SetCurrentTool(BaseTool tool)
   at Pinta.Core.ToolManager.HandleToolBoxToolItemClicked(Object sender, EventArgs e)
   at System.RuntimeMethodHandle.InvokeMethod(Object target, Void** arguments, Signature sig, Boolean isConstructor)
   at System.Reflection.MethodInvoker.Invoke(Object obj, IntPtr* args, BindingFlags invokeAttr)
   --- End of inner exception stack trace ---
   at System.Reflection.MethodInvoker.Invoke(Object obj, IntPtr* args, BindingFlags invokeAttr)
   at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
   at System.Delegate.DynamicInvokeImpl(Object[] args)
   at GLib.Signal.ClosureInvokedCB(Object o, ClosureInvokedArgs args)
   at GLib.SignalClosure.MarshalCallback(IntPtr raw_closure, IntPtr return_val, UInt32 n_param_vals, IntPtr param_values, IntPtr invocation_hint, IntPtr marshal_data)
```

[Cameron White (cameronwhite91)]

I haven't been able to reproduce this yet, but this may have been fixed in the master branch since the GTK4 port changed a bit of that code

https://github.com/PintaProject/Pinta/blob/master/Pinta.Core/Managers/ToolManager.cs#L249
vs
https://github.com/PintaProject/Pinta/blob/gtk3/Pinta.Core/Managers/ToolManager.cs#L242