MdeModulePkg/Bds: Check variable name even *if* OptionNumber is NULL

MdeModulePkg/Bds: Check variable name even *if* OptionNumber is NULL

Current implementation skips to check whether the last four
characters are digits when the OptionNumber is NULL.
Even worse, it may incorrectly return FALSE when OptionNumber is
NULL.

The patch fixes it to always check the variable name even
OptionNumber is NULL.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>