osc: apply boxvideo margins to the window controls

It seems logical to account for the window controls if `boxvideo`
is in use (which has the effect of reducing the size of the video
so that the osc is not covering the video).

DOCS/man/osc.rst

@@ -331,7 +331,9 @@ Configurable Options
     default values.)
 
     Currently, this is supported for the ``bottombar`` and ``topbar`` layout
-    only. The other layouts do not change if this option is set.
+    only. The other layouts do not change if this option is set. Separately,
+    if window controls are present (see below), they will be affected
+    regardless of which osc layout is in use.
 
     The border is static and appears even if the OSC is configured to appear
     only on mouse interaction. If the OSC is invisible, the border is simply

player/lua/osc.lua

@@ -1054,6 +1054,9 @@ function window_controls(alignment, topbar)
     if topbar then
         -- The title is already there as part of the top bar
         return
+    else
+        -- Apply boxvideo margins to the control bar
+        osc_param.video_margins.t = wsc_geo.h / osc_param.playresy
     end
 
     -- Window Title