Support has_minimum/has_maximum in horizontal listboxes

data/gui/schema.cfg

@@ -1475,6 +1475,16 @@
                                         type="scrollbar_mode"
                                         default=initial_auto
                                     [/key]
+                                    [key]
+                                        name="has_minimum"
+                                        type="bool"
+                                        default=true
+                                    [/key]
+                                    [key]
+                                        name="has_maximum"
+                                        type="bool"
+                                        default=true
+                                    [/key]
                                 [/tag]
                                 [tag]
                                     name="horizontal_scrollbar"

src/gui/widgets/listbox.cpp

@@ -992,6 +992,10 @@ twidget* tbuilder_listbox::build() const
  *                                     must have the same number of columns as
  *                                     the 'list_definition'. $
  *
+ *     has_minimum & bool & true &     If false, less than one row can be selected. $
+ *
+ *     has_maximum & bool & true &     If false, more than one row can be selected. $
+ *
  * @end{table}
  * @begin{tag}{name="header"}{min=0}{max=1}{super="gui/window/resolution/grid"}
  * @end{tag}{name="header"}
@@ -1023,6 +1027,8 @@ tbuilder_horizontal_listbox::tbuilder_horizontal_listbox(const config& cfg)
 			  get_scrollbar_mode(cfg["horizontal_scrollbar_mode"]))
 	, list_builder(nullptr)
 	, list_data()
+	, has_minimum_(cfg["has_minimum"].to_bool(true))
+	, has_maximum_(cfg["has_maximum"].to_bool(true))
 {
 	const config& l = cfg.child("list_definition");
 
@@ -1069,7 +1075,7 @@ twidget* tbuilder_horizontal_listbox::build() const
 	return widget;
 #else
 	tlistbox* widget
-			= new tlistbox(true, true, tgenerator_::horizontal_list, true);
+			= new tlistbox(has_minimum_, has_maximum_, tgenerator_::horizontal_list, true);
 
 	init_control(widget);
 

src/gui/widgets/listbox.hpp

@@ -428,6 +428,8 @@ struct tbuilder_horizontal_listbox : public tbuilder_control
 	 * serialize the data in the config, so the config is no longer required.
 	 */
 	std::vector<string_map> list_data;
+
+	bool has_minimum_, has_maximum_;
 };
 
 } // namespace implementation