gtkui: autosort is not triggered when dragging items to another play list

[rsekman]

Steps to reproduce the problem

Using gtkui2, create two playlists. Add some items to both. Sort one of them and enable autosort. Drag some items from the other playlist to it.

What's going on? Describe the problem in as much detail as possible.

Expected behaviour: The items are inserted where they would be if they were added using Add files. That is, the playlist is autosorted.

Actual behaviour: The items are appended at the end of the playlist

Information about the software:

Deadbeef version: built from master OS: Linux naoetsu 5.16.14-arch1-1 #1 SMP PREEMPT Fri, 11 Mar 2022 17:40:36 +0000 x86_64 GNU/Linux