ShellPkg: Do not mix status when executing a command

The function InternalShellExecuteDevicePath() did not differentiate an error occuring during the preparation of an image and an error occurring during its execution.

A use case of the issue was when a EFI application was called in a EFI Shell script. If the EFI application was returning an error then the NSH script stopped its execution. While the EFI Shell specification says the script should continue its execution (see 4.2 Error Handling).

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Olivier Martin <olivier.martin@arm.com>
Reviewed-by: Jaben Carsey <Jaben.Carsey@intel.com>


git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@15523 6f19259b-4bc3-4df7-8a09-765794883524