Fixed a bug where diassembling an instruction that had a prefix would cause LLVM to identify a 1-byte instruction, but then upon querying it for that 1-byte instruction would cause an undefined opcode.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@189698 91177308-0d34-0410-b5e6-96231b3b80d8