Update question validation logic, move the check pointer from after user input to...

Update question validation logic, move the check pointer from after user input to after finish call the CHANGING callback.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Eric Dong <eric.dong@intel.com>
Reviewed-by: Liming, Gao <liming.gao@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@15468 6f19259b-4bc3-4df7-8a09-765794883524