Can't open a lone zobj properly without opening a rom first

[Dragorn421]

Someone who isn't me had an issue viewing a single .zobj until they opened a rom

error trace:

Consultez la fin de ce message pour plus de détails sur l'appel du débogage
juste-à-temps (JIT) à la place de cette boîte de dialogue.

************** Texte de l'exception **************
System.NullReferenceException: Object reference not set to an instance of an object.
   at Z64.Forms.SkeletonViewerForm..ctor(Z64Game game, Int32 curSegment) in D:\Z64Utils\Z64Utils\Forms\SkeletonViewerForm.cs:line 75
   at Z64.Forms.ObjectAnalyzerForm.openSkeletonViewer() in D:\Z64Utils\Z64Utils\Forms\ObjectAnalyzerForm.cs:line 679
   at Z64.Forms.ObjectAnalyzerForm.listView_map_DoubleClick(Object sender, EventArgs e) in D:\Z64Utils\Z64Utils\Forms\ObjectAnalyzerForm.cs:line 176
   at System.Windows.Forms.Control.OnDoubleClick(EventArgs e)
   at System.Windows.Forms.ListView.WndProc(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, WM msg, IntPtr wparam, IntPtr lparam)

this puts the error at
https://github.com/zeldaret/Z64Utils/blob/v2.2.1/Z64Utils/Forms/SkeletonViewerForm.cs#L75

or in master at:

Z64Utils/Z64Utils/Forms/SkeletonViewerForm.cs

Line 76 in a960313

_renderer.Memory.Segments[4] = F3DZEX.Memory.Segment.FromBytes("gameplay_keep", game.GetFileByName("gameplay_keep").Data);

It gave me the hint to suggest loading a rom before opening the zobj
And that worked

So there should be a check to not try to load gkeep if it's not available (no rom loaded)