MdeModulePkg SmiHandlerProfile: Fix no PDB case handling incorrectly
    
    REF: https://bugzilla.tianocore.org/show_bug.cgi?id=569
    
    The PdbStringOffset should be set to 0 for no PDB case,
    then SmiHandlerProfileInfo can use it to know whether
    there is PCD info or not.
    
    Cc: Jiewen Yao <jiewen.yao@intel.com>
    Contributed-under: TianoCore Contribution Agreement 1.0
    Signed-off-by: Star Zeng <star.zeng@intel.com>
    Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>