Crash with 1.7.1

[Nico]

With the update to 1.7.1 it happens to me, that Pinta crashes sometimes. I cannot reproduce it, but this time it was when moving a layer position. Here is the stack trace:

```
System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.NullReferenceException: Object reference not set to an instance of an object
  at Cairo.Context..ctor (Cairo.Surface surface) [0x00000] in <de76a7ad0aa84dfe82dca84f7376bcb1>:0
  at Pinta.Core.CairoExtensions.Clear (Cairo.ImageSurface surface) [0x00001] in <58b378bd67ff4eb68b9cfec964986533>:0
  at Pinta.Gui.Widgets.CanvasRenderer.CreateOffsetLayer (Pinta.Core.Layer original) [0x0000e] in <ffdcf9c12be04ea99b21bf86f5860bee>:0
  at Pinta.Gui.Widgets.CanvasRenderer.Render (System.Collections.Generic.List`1[T] layers, Cairo.ImageSurface dst, Gdk.Point offset) [0x000b2] in <ffdcf9c12be04ea99b21bf86f5860bee>:0
  at Pinta.Gui.Widgets.LayersListWidget.Reset () [0x000db] in <ffdcf9c12be04ea99b21bf86f5860bee>:0
  at Pinta.Gui.Widgets.LayersListWidget.HandleHistoryItemAdded (System.Object sender, System.EventArgs e) [0x00001] in <ffdcf9c12be04ea99b21bf86f5860bee>:0
  at (wrapper delegate-invoke) System.EventHandler`1[Pinta.Core.HistoryItemAddedEventArgs].invoke_void_object_TEventArgs(object,Pinta.Core.HistoryItemAddedEventArgs)
  at Pinta.Core.HistoryManager.OnHistoryItemAdded (Pinta.Core.BaseHistoryItem item) [0x0001b] in <58b378bd67ff4eb68b9cfec964986533>:0
  at Pinta.Core.DocumentWorkspaceHistory.PushNewItem (Pinta.Core.BaseHistoryItem newItem) [0x00123] in <58b378bd67ff4eb68b9cfec964986533>:0
  at Pinta.Core.HistoryManager.PushNewItem (Pinta.Core.BaseHistoryItem newItem) [0x00010] in <58b378bd67ff4eb68b9cfec964986533>:0
  at Pinta.Tools.MoveSelectedTool.OnFinishTransform (Cairo.Matrix transform) [0x00047] in <03eff47cd58e45dfb61eb4d487f72bfb>:0
  at Pinta.Tools.BaseTransformTool.OnMouseUp (Gtk.DrawingArea canvas, Gtk.ButtonReleaseEventArgs args, Cairo.PointD point) [0x0001b] in <03eff47cd58e45dfb61eb4d487f72bfb>:0
  at Pinta.Core.BaseTool.DoMouseUp (Gtk.DrawingArea canvas, Gtk.ButtonReleaseEventArgs args, Cairo.PointD point) [0x00033] in <58b378bd67ff4eb68b9cfec964986533>:0
  at Pinta.Gui.Widgets.PintaCanvas+<>c__DisplayClass8_0.<.ctor>b__3 (System.Object sender, Gtk.ButtonReleaseEventArgs e) [0x00038] in <ffdcf9c12be04ea99b21bf86f5860bee>:0
  at (wrapper managed-to-native) System.Reflection.RuntimeMethodInfo.InternalInvoke(System.Reflection.RuntimeMethodInfo,object,object[],System.Exception&)
  at System.Reflection.RuntimeMethodInfo.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x0006a] in <62b430b945fa49a19a75382ef03e7bed>:0
   --- End of inner exception stack trace ---
  at System.Reflection.RuntimeMethodInfo.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00083] in <62b430b945fa49a19a75382ef03e7bed>:0
  at System.Reflection.MethodBase.Invoke (System.Object obj, System.Object[] parameters) [0x00000] in <62b430b945fa49a19a75382ef03e7bed>:0
  at System.Delegate.DynamicInvokeImpl (System.Object[] args) [0x000e7] in <62b430b945fa49a19a75382ef03e7bed>:0
  at System.MulticastDelegate.DynamicInvokeImpl (System.Object[] args) [0x00008] in <62b430b945fa49a19a75382ef03e7bed>:0
  at System.Delegate.DynamicInvoke (System.Object[] args) [0x00000] in <62b430b945fa49a19a75382ef03e7bed>:0
  at GLib.Signal.ClosureInvokedCB (System.Object o, GLib.ClosureInvokedArgs args) [0x0007d] in <ed39f21b9e9343dcbd442a17ad356a9f>:0
  at GLib.Signal+SignalClosure.Invoke (GLib.ClosureInvokedArgs args) [0x0000c] in <ed39f21b9e9343dcbd442a17ad356a9f>:0
  at GLib.Signal+SignalClosure.MarshalCallback (System.IntPtr raw_closure, GLib.Value* return_val, System.UInt32 n_param_vals, GLib.Value* param_values, System.IntPtr invocation_hint, System.IntPtr marshal_data) [0x000b1] in <ed39f21b9e9343dcbd442a17ad356a9f>:0
```

[Cameron White (cameronwhite91)]

Thanks for the report! I haven't been able to reproduce it yet
To confirm, have you encountered this in v1.7 or only in 1.7.1?

[Nico (nicohood)]

Only in 1.7.1 at least twice.

[Cameron White (cameronwhite91)]

I've found repro steps:

- Make a selection and use Move Selected Pixels to move it around
- Use Image -> Resize Image to change the size, e.g. to 105%
- Try to use Move Selected Pixels again

I'll mark the other issue as a duplicate since they look like the same crash.

[Cameron White (cameronwhite91)]

Fixed by https://github.com/PintaProject/Pinta/commit/46dca467420ce435e1d4406fe6ba136505a7b99d (this issue wasn't in the gtk3 / master branch)