Merge pull request #1846 from psychon/menubar-no-icon-theme

menubar.icon_theme: Never use nil as icon theme name

lib/menubar/icon_theme.lua

@@ -70,7 +70,7 @@ local get_default_icon_theme_name = function()
             end
         end
     end
-    return nil
+    return "hicolor"
 end
 
 local icon_theme = { mt = {} }