Security/OpalHii.c: Handle NULL Request or Request with no elements

Security/OpalHii.c: Handle NULL Request or Request with no elements

According to UEFI spec, for the ExtractConfig function in
EFI_HII_CONFIG_ACCESS_PROTOCOL,If a NULL is passed in for the Request
field or if a ConfigHdr is passed in with no request elements, all of
the settings being abstracted by this function will be returned in the
Results field.

The implementation of ExtractConfig function in OpalHii.c misses to
handle above cases.This patch is to do the enhancements.

Cc: Chao Zhang <chao.b.zhang@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Dandan Bi <dandan.bi@intel.com>
Reviewed-by: Eric Dong <eric.dong@intel.com>