Fix split root removed accidentally

While handleStartResult, if it start unsucessful, the root task might
be remove and cause split root removed accidentally. It will cause
crash next time active split screen. We should avoid the task removed
here if it is creadted by organizer.

Bug: 234406935
Test: manual
Test: pass existing tests
Change-Id: I383682625fa0b90ec8d59873f813ed46162eef12