Make the client.null_instrument test pass with -disable_traces
Make the client.null_instrument test pass with -disable_traces

Review URL: https://codereview.appspot.com/6851134

git-svn-id: ed337ca7cdb08c0ba29d8fe58632bb7686892c2d@1747 49cc7528-f6fd-11dd-9d1a-b59b2e1864b6

rnk/dynamorio,rnk/dynamorio,rnk/dynamorio,rnk/dynamorio,rnk/dynamorio