MdeModulePkg:Make the logic in ConfigRouting.c clear and safe

MdeModulePkg:Make the logic in ConfigRouting.c clear and safe

The BlockData is expected to be NULL when to call function
IsThisOpcodeRequired in each opcode,but now exists case that the
Blockdata not be cleaned,then will be used in other opcode.it
is not correct,now add the check before use.

The comments and logic in function IsThisOpcodeRequired are not
consistent,now refine the code to make the logic clear.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Dandan Bi <dandan.bi@intel.com>
Reviewed-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@19749 6f19259b-4bc3-4df7-8a09-765794883524