[aws-ecr-cleaner] Panic when there are no images to delete

[VJftw]

2017/12/20 15:20:16 Deleting 0 images: 
panic: runtime error: slice bounds out of range

goroutine 1 [running]:
main.main()
	/go/src/aws-ecr-cleaner/main.go:109 +0xfbf

Seemingly can't iterate through an empty slice.