context_menu.lua: add a missing return

The space key selects the current item so it shouldn't also try to
activate items with titles starting with space.

Author: guidocella

player/lua/context_menu.lua

@@ -571,6 +571,7 @@ local function activate_shortcut(info)
 
    if info.key_text == " " then
        activate_focused_item(true)
+       return
    end
 
    for i, item in ipairs(items[focused_level]) do