TOOLS/autocrop.lua: log a more accurate warning

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.

TOOLS/lua/autocrop.lua

@@ -107,14 +107,18 @@ function is_enough_time(seconds)
     return playtime_remaining and time_needed < playtime_remaining
 end
 
-function is_cropable()
-    for _, track in pairs(mp.get_property_native('track-list')) do
-        if track.type == 'video' and track.selected then
-            return not track.albumart
-        end
+function is_cropable(time_needed)
+    if mp.get_property_native('current-tracks/video/image') ~= false then
+        mp.msg.warn("autocrop only works for videos.")
+        return false
     end
 
-    return false
+    if not is_enough_time(time_needed) then
+        mp.msg.warn("Not enough time to detect crop.")
+        return false
+    end
+
+    return true
 end
 
 function remove_filter(label)
@@ -142,18 +146,9 @@ function cleanup()
 end
 
 function detect_crop()
-
-    -- If it's not cropable, exit.
-    if not is_cropable() then
-        mp.msg.warn("autocrop only works for videos.")
-        return
-    end
-
-    -- Verify if there is enough time to detect crop.
     local time_needed = options.detect_seconds
 
-    if not is_enough_time(time_needed) then
-        mp.msg.warn("Not enough time to detect crop.")
+    if not is_cropable(time_needed) then
         return
     end
 
@@ -282,8 +277,7 @@ function on_start()
         -- Verify if there is enough time for autocrop.
         local time_needed = options.auto_delay + options.detect_seconds
 
-        if not is_enough_time(time_needed) then
-            mp.msg.warn("Not enough time for autocrop.")
+        if not is_cropable(time_needed) then
             return
         end