Application crashes when user tries to save a scene which is already deleted from resource manager.

[Kanoot]

1. Launch application.

2. Create main folder.

3. Create sub folders and sprite scene.

4. Delete main folder.

5. Ctrl+ S.

   -- Result: Application crashes when user tries to save a scene which is already deleted from resource manager

This happens 3/3 times.

Video is attached here:
https://drive.google.com/file/d/0B2b3lCCE3OwtazFidnUtR0x6aWs/edit?usp=sharing

Build version used: SpriteBuilder-1.1.0-beta.2

Used:

• MacBook Pro
  Version: OS X 10.9.2(13C64).
  Processor: 2.66 GHz Intel Core i7
• MacBook Pro
  Version: OS X 10.9.1