Prevent to add files to list more than once

The steps:
1. Create a new repository
2. git add 3 files
3. Select any 2 files and right click on them, then commit
4. CGitStatusListCtrl shows 3 added files twice

Signed-off-by: Yue Lin Ho <b8732003@student.nsysu.edu.tw>
Signed-off-by: Sven Strickroth <email@cs-ware.de>
Fix possible out-of-bounds access

Signed-off-by: Sven Strickroth <email@cs-ware.de>
Fix some possible resource leaks

Signed-off-by: Sven Strickroth <email@cs-ware.de>
Split change log into two files

Signed-off-by: Sven Strickroth <email@cs-ware.de>
Constify and staticify methods

Signed-off-by: Sven Strickroth <email@cs-ware.de>
Drop unused code

Signed-off-by: Sven Strickroth <email@cs-ware.de>
Check data != nullptr on all code paths

Signed-off-by: Sven Strickroth <email@cs-ware.de>
Drop ShortName attributes

Signed-off-by: Sven Strickroth <email@cs-ware.de>