MdeModulePkg/Browser: Fix conflicting policy in getting default of checkbox

MdeModulePkg/Browser: Fix conflicting policy in getting default of checkbox

We have added a new policy to get default value for question:
get default from other default id if current default is not specified.
But when getting default value for checkbox, if the default
flag is not set, it will set the default value to FALSE for checkbox.
This behavior in checkbox conflicts with the new added policy,
so now we move this behavior to the end of getting default form other
default id.

Cc: Liming Gao <liming.gao@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Dandan Bi <dandan.bi@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>