[birt-dev]CheckIn: Fix unit test error.

["Wei Zhao \(Shang\)" <wei.zhao@xxxxxxxxxxx>]

Title: [birt-dev]CheckIn: Fix unit test error.

- Summary:
AchiveReader in reportDocumentReader maybe used more than once, so we shoule check the achiveReader is be shared before close it.

- Bugzilla Bug (s) Resolved:
NONE

- Description:
AchiveReader in reportDocumentReader maybe used more than once, so we shoule check the achiveReader is be shared before close it.

- Tests Description  :
Unit Test

- Notes to Build Team:

- Notes to Developers:

- Notes to QA:  
 
- Notes to Documentation:  

- Files Edited:
"/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/api/impl/EngineTask.java"
"/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/api/impl/ReportDocumentReader.java"

- Files Added:

- Files Deleted

-Wei Zhao(Shanghai)