Add check to inst visitor
Add check to inst visitor

Just tripped on this, a malformed instruction region could make you
endlessly loopy.

Change-Id: Ib65e147c4cd8fe02328bc62aee2bbecfde604455

treadstoneproject/artinst,treadstoneproject/artinst,treadstoneproject/artinst,treadstoneproject/artinst,treadstoneproject/artinst