Stop workflow when 0 faces found

[peterjakubowski]

When step 1: detect faces completes and 0 faces are found, the workflow should stop. Currently, the workflow will move on to step 2: label faces and display a message that 0 faces were labeled and the workflow is complete. Update the workflow so it: 1) displays a workflow complete message at step 1; and 2) does not move on to step 2.