Do not assert when the device path node length is invalid.

Because IsDevicePathValid() calls this API we should leave the device path validation in the caller.

(Sync patch r16555 from main trunk.)

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>


git-svn-id: svn://svn.code.sf.net/p/edk2/code/branches/UDK2014.SP1/MdePkg@16557 6f19259b-4bc3-4df7-8a09-765794883524