x86 fault handler does not know about movb

mov byte instruction is not known for fault handler and therefore
it cannot catch null pointer exception represented by this instruction.
As a result implicit null check does not work.

Change-Id: I45d6056f838d1568fce3de58218437fc12d1c45b
Signed-off-by: Serguei Katkov <serguei.i.katkov@intel.com>