AppButton: Fix drag to dock

[danirabbit]

Fixes #614

Don't close the menu until after drag operation is completed

[ryonakano]

For me the dock doesn't seem to accept DND and can't confirm if the issue is fixed 🤔

Screencast.From.2025-05-29.20-52-56.mp4

[danirabbit]

@ryonakano I should mention I'm testing on Wayland. I didn't test for X11

[ryonakano]

Yes, I also tested on Wayland. It looks like this not always happens but keeping apps in the dock from the secondary menu does not seem to persistent when it happens and opening the secondary menu again disappear the app from the dock:

Screencast.From.2025-05-30.22-10-56.mp4

But this disappear issue is reproducible in latest master too (81336c1) thus I don't think it would be a regression from this branch.

[ryonakano]

For me the dock doesn't seem to accept DND and can't confirm if the issue is fixed 🤔

For me this happens about 80% on Wayland and 100% on X, so I can't confirm if this PR does fix the linked issue actually