This reorders some code and checks the image track-list sub-property
instead of the albumart one, so that when playing audio without enough
playtime-remaining and images, the "autocrop only works for videos."
warning is logged instead of the "Not enough time to detect crop." one.
It also avoids repeating this warning twice in the code.
As of e16d0dd15d current-tracks returns a video track even when
lavfi-complex is used, so the track-list loop in is_cropable can be
replaced with just checking current-tracks/video while still cropping
videos with lavfi-complex.