Avoid TypeError if build output array is empty
Avoid TypeError if build output array is empty

Change-type: patch
Signed-off-by: Kyle Harding <3c25b01657254677d3e1a8fd1f0742c5d489bd39@balena.io>
resin-io/resin-preload-image-script,resin-io/resin-preload-image-script