dock: call wAppIconPaint from dockIconPaint instead of raw backend

dockIconPaint was calling wm_backend->appicon_paint directly, which
bypasses wAppIconPaint and its appicon_paint_dock_dots call. This meant
docked icons never got their dots drawn at startup.

Call wAppIconPaint instead so the full paint path (tile + dots + stipple)
executes for all docked appicons.

src/dock.c

@@ -1362,7 +1362,7 @@ static void dockIconPaint(WAppIcon *btn)
 	} else if (wIsADrawer(btn)) {
 		wDrawerIconPaint(btn);
 	} else {
-		wm_backend->appicon_paint(btn);
+		wAppIconPaint(btn);
 		save_appicon(btn);
 	}
 }