centered-cinnamon-dock: fix dock becoming invisible after a workspace switch

[Rogue1-OC]

Problem

With autoHide: false and hideOnFullscreen: true (the default mode), the dock panel becomes invisible after any workspace switch (keyboard Ctrl+Alt+←/→ or a 3-finger touchpad swipe). The actor is still show()n but left at opacity = 0, so the dock vanishes until something else (closing a fullscreen window, or a hover that calls showPanel) happens to restore it.

Reproduced on Cinnamon 6.6.7 (X11).

Root cause

In the workspace-switched handler (6.4/extension.js, ~line 1186) the panel is blanked to recompute geometry, but nothing restores it on the autoHide:false / no-fullscreen path:

state.isHidden = false;
panel.actor.opacity = 0;          // blank to recompute
panel.actor.show();
checkAndApplyStyle(panel, true);  // -> applyStyle() reads back opacity 0 and re-applies it

1. applyStyle() computes savedOpacity = state.isHidden ? 0 : panel.actor.opacity. Since opacity was just set to 0 and isHidden is false, savedOpacity is 0, and it re-applies that 0 — preserving the invisible state.
2. The follow-up Mainloop.timeout_add(100, …) only ever hides (autoHide/hideOnFullscreen); with autoHide:false and no fullscreen window it does nothing.
3. startSizeMonitoring only corrects opacity when it is strictly between 0 and 255 (opacity > 0 && opacity < 255), so exactly-0 is never recovered.

Fix

Restore opacity after the style recompute. The existing 100ms timeout still re-hides correctly when hideOnFullscreen/autoHide require it, so fullscreen-hide behavior is unchanged.

Verified on Cinnamon 6.6.7: the dock now stays visible across workspace switches, and hideOnFullscreen still hides it when a fullscreen window is focused.

I kept this to the minimal code change. The metadata.json version is currently 1.2 while the CHANGELOG already lists a 1.3 entry, so I left the version bump / changelog to you to avoid muddying that — happy to add it if you prefer.

cc @mostlynick3 (original author)

[mostlynick3]

Good catch, thanks! I think it'd be safest if you bump both the changelog and metadata.json to 1.4 with your changes, so we skip my muddied waters :)