Fix disasm assertions for undefined instructions.
Fix disasm assertions for undefined instructions.

BUG=none
TEST=none

Review URL: https://chromiumcodereview.appspot.com/9228006
Patch from Martyn Capewell <m.m.capewell@googlemail.com>.

git-svn-id: b158db1e4b4ab85d4c9e510fdef4b1e8c614b15b@10498 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh