Simplify handling of the "tried to pull an image but found nothing" case in newBuilder
Simplify handling of the "tried to pull an image but found nothing" case in newBuilder

resolveImage already either returns an image, or an error; never (nil, nil, nil),
so this is dead code; drop it.

Should not change behavior.

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

Closes: #909
Approved by: rhatdan

nalind/buildah,rhatdan/buildah,rhatdan/buildah,nalind/buildah-1,nalind/buildah-1,rhatdan/buildah,ipbabble/buildah,projectatomic/buildah,ipbabble/buildah,TomSweeneyRedHat/buildah,TomSweeneyRedHat/buildah,nalind/buildah-1,projectatomic/buildah,nalind/buildah,projectatomic/buildah,TomSweeneyRedHat/buildah