Unable To Create New Assets Without Specifying Extension

[Nocxr]

Issue description:

Trying to create an asset of any type in the content window results in ignoring the enter key or rejecting the creation if clicked off unless the user specifies some sort of extension.

(I am trying to hit enter in the video on the first asset creation)

Steps to reproduce:

1. Right click in the content window and try to create any new asset without specifying an extension

Minimal reproduction project:

1. New or existing project

Flax version:

1.0.6214 (last commit pulled: 8198b73)

2020.12.22-18.16-1.mp4

[Nocxr]

Output log is spitting this out when trying to hit enter on an asset without an extension:

[ 01:55:04.010 ]: [Warning] Exception has been thrown during Window.OnKeyDown. Index was outside the bounds of the array.
Stack strace:
  at FlaxEngine.StringUtils.NormalizeExtension (System.String extension) [0x00000] in F:\Flax\FlaxEngine\Source\Engine\Utilities\StringUtils.cs:95 
  at FlaxEditor.Windows.ContentWindow.Rename (FlaxEditor.Content.ContentItem item, System.String newShortName) [0x00024] in F:\Flax\FlaxEngine\Source\Editor\Windows\ContentWindow.cs:300 
  at FlaxEditor.Windows.ContentWindow.<Rename>b__37_0 (FlaxEditor.GUI.RenamePopup renamePopup) [0x00000] in F:\Flax\FlaxEngine\Source\Editor\Windows\ContentWindow.cs:250 
  at FlaxEditor.GUI.RenamePopup.OnEnd () [0x0001d] in F:\Flax\FlaxEngine\Source\Editor\GUI\Popups\RenamePopup.cs:135 
  at FlaxEditor.GUI.RenamePopup.OnKeyDown (FlaxEngine.KeyboardKeys key) [0x00005] in F:\Flax\FlaxEngine\Source\Editor\GUI\Popups\RenamePopup.cs:147 
  at FlaxEngine.GUI.ContainerControl.OnKeyDown (FlaxEngine.KeyboardKeys key) [0x00021] in F:\Flax\FlaxEngine\Source\Engine\UI\GUI\ContainerControl.cs:1013 
  at FlaxEngine.Window.Internal_OnKeyDown (FlaxEngine.KeyboardKeys key) [0x00012] in F:\Flax\FlaxEngine\Source\Engine\Platform\Window.cs:215 
[ 01:55:04.011 ]: [Error] Exception has been thrown during Window.OnKeyDown.
Index was outside the bounds of the array