osc.lua: fix window controls not showing in fullscreen

Author: kasper93

DOCS/man/osc.rst

@@ -404,7 +404,8 @@ Configurable Options
     render OSD into the unscaled video.
 
 ``windowcontrols``
-    Default: auto (Show window controls if there is no window border)
+    Default: auto (Show window controls if there is no window border/title-bar or
+    in the fullscreen mode.)
 
     Whether to show window management controls over the video, and if so,
     which side of the window to place them. This may be desirable when the

player/lua/osc.lua

@@ -650,7 +650,7 @@ end
 local function window_controls_enabled()
     local val = user_opts.windowcontrols
     if val == "auto" then
-        return not (state.border and state.title_bar)
+        return state.fullscreen or not state.border or not state.title_bar
     else
         return val ~= "no"
     end