asynctypes-685526: Properly check cursor value
asynctypes-685526: Properly check cursor value

Once again caught by a truthyness bug. If the tester set cursor=0, then
we would previously not set the cursor position. With this better test
we do.

Signed-off-by: Joe Walker <7a17872fbb32c7d760c9a16ee3076daead11efcf@mozilla.com>

mozilla/gcli,joewalker/gcli,mozilla/gcli,joewalker/gcli,mozilla/gcli