Refine the logic when return success, should not clean the buffer in this case.

Signed-off-by: Eric Dong <eric.dong@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>

git-svn-id: svn://svn.code.sf.net/p/edk2/code/trunk/edk2/MdeModulePkg@15169 6f19259b-4bc3-4df7-8a09-765794883524
Update password process logic, if password without interactive attribute, the first byte of buffer is zero means this password not has preexist value.

Signed-off-by: Eric Dong <eric.dong@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>

git-svn-id: svn://svn.code.sf.net/p/edk2/code/trunk/edk2/MdeModulePkg@15170 6f19259b-4bc3-4df7-8a09-765794883524