ShellPkg: InternalShellExecuteDevicePath: avoid memory leaks
    
    Contributed-under: TianoCore Contribution Agreement 1.0
    Signed-off-by: Brendan Jackman <Brendan.Jackman@arm.com>
    Reviewed-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@15224 6f19259b-4bc3-4df7-8a09-765794883524