[birt-dev]CheckIn: [2.1.3]update the code to ensure no NPE will be throw

["Wei Wang" <wwang@xxxxxxxxxxx>]

Title: [birt-dev]CheckIn: [2.1.3]update the code to ensure no NPE will be thrownafter the archive file has been closed.

- Summary:
[2.1.3]update the code to ensure no NPE will be thrownafter the archive file has been closed.

- Bugzilla Bug (s) Resolved:
None

- Description:
[2.1.3]update the code to ensure no NPE will be thrownafter the archive file has been closed.

- Tests Description  :
Unit Test

- Notes to Build Team:
None

- Notes to Developers:
None

- Notes to QA:  
None

- Notes to Documentation:  
None

- Files Edited:
"/org.eclipse.birt.core/src/org/eclipse/birt/core/archive/compound/ArchiveFile.java"

- Files Added:
None

- Files Deleted
None

- Wei Wang
Actuate Software(Shanghai) Co.,Ltd