ShellPkg: Refine the code logic of mv.c.

ShellPkg: Refine the code logic of mv.c.

When doing the mv we should check whether source is 'above' dest on file path tree. This patch make the check logic more precise.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Qiu Shumin <shumin.qiu@intel.com>
Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>
Reviewed-by: Samer El-Haj-Mahmoud <elhaj@hp.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@17750 6f19259b-4bc3-4df7-8a09-765794883524