AppOpsService.dump() over-used iterator fix

The dump() was using the variable i in both the
inner and outer loop, causing the list of watchers
that were dumped() to be incorrect (and, in unlucky cases,
never-ending).

Bug: 152023451
Bug: 151193211
Test: compiles. And adb shell dumpsys appops still works.
Change-Id: If098f70b386fdc420d970013e6fe9bcbb640ca4b