Fix potential use of old names in group and engine name sorters

This could result in violation of strict weak ordering

src/build_vehicle_gui.cpp

@@ -126,6 +126,9 @@ static bool EngineIntroDateSorter(const EngineID &a, const EngineID &b)
 	return _engine_sort_direction ? r > 0 : r < 0;
 }
 
+/* cached values for EngineNameSorter to spare many GetString() calls */
+static EngineID _last_engine[2] = { INVALID_ENGINE, INVALID_ENGINE };
+
 /**
  * Determines order of engines by name
  * @param a first engine to compare
@@ -134,17 +137,16 @@ static bool EngineIntroDateSorter(const EngineID &a, const EngineID &b)
  */
 static bool EngineNameSorter(const EngineID &a, const EngineID &b)
 {
-	static EngineID last_engine[2] = { INVALID_ENGINE, INVALID_ENGINE };
-	static char     last_name[2][64] = { "\0", "\0" };
+	static char     last_name[2][64] = { "", "" };
 
-	if (a != last_engine[0]) {
-		last_engine[0] = a;
+	if (a != _last_engine[0]) {
+		_last_engine[0] = a;
 		SetDParam(0, a);
 		GetString(last_name[0], STR_ENGINE_NAME, lastof(last_name[0]));
 	}
 
-	if (b != last_engine[1]) {
-		last_engine[1] = b;
+	if (b != _last_engine[1]) {
+		_last_engine[1] = b;
 		SetDParam(0, b);
 		GetString(last_name[1], STR_ENGINE_NAME, lastof(last_name[1]));
 	}
@@ -1302,6 +1304,9 @@ struct BuildVehicleWindow : Window {
 
 		this->SelectEngine(sel_id);
 
+		/* invalidate cached values for name sorter - engine names could change */
+		_last_engine[0] = _last_engine[1] = INVALID_ENGINE;
+
 		/* make engines first, and then wagons, sorted by selected sort_criteria */
 		_engine_sort_direction = false;
 		EngList_Sort(&this->eng_list, TrainEnginesThenWagonsSorter);

src/company_gui.cpp

@@ -556,6 +556,9 @@ static const int LEVEL_WIDTH = 10; ///< Indenting width of a sub-group in pixels
 
 typedef GUIList<const Group*> GUIGroupList;
 
+/* cached values for GroupNameSorter to spare many GetString() calls */
+static const Group *_last_group[2] = { nullptr, nullptr };
+
 /** Company livery colour scheme window. */
 struct SelectCompanyLiveryWindow : public Window {
 private:
@@ -621,17 +624,16 @@ private:
 
 	static bool GroupNameSorter(const Group * const &a, const Group * const &b)
 	{
-		static const Group *last_group[2] = { nullptr, nullptr };
 		static char         last_name[2][64] = { "", "" };
 
-		if (a != last_group[0]) {
-			last_group[0] = a;
+		if (a != _last_group[0]) {
+			_last_group[0] = a;
 			SetDParam(0, a->index);
 			GetString(last_name[0], STR_GROUP_NAME, lastof(last_name[0]));
 		}
 
-		if (b != last_group[1]) {
-			last_group[1] = b;
+		if (b != _last_group[1]) {
+			_last_group[1] = b;
 			SetDParam(0, b->index);
 			GetString(last_name[1], STR_GROUP_NAME, lastof(last_name[1]));
 		}
@@ -669,6 +671,10 @@ private:
 			}
 
 			list.ForceResort();
+
+			/* invalidate cached values for name sorter - group names could change */
+			_last_group[0] = _last_group[1] = nullptr;
+
 			list.Sort(&GroupNameSorter);
 
 			AddChildren(&list, INVALID_GROUP, 0);

src/group_gui.cpp

@@ -106,20 +106,22 @@ static const NWidgetPart _nested_group_widgets[] = {
 	EndContainer(),
 };
 
+/* cached values for GroupNameSorter to spare many GetString() calls */
+static const Group *_last_group[2] = { nullptr, nullptr };
+
 /** Sort the groups by their name */
 bool GroupNameSorter(const Group * const &a, const Group * const &b)
 {
-	static const Group *last_group[2] = { nullptr, nullptr };
 	static char         last_name[2][64] = { "", "" };
 
-	if (a != last_group[0]) {
-		last_group[0] = a;
+	if (a != _last_group[0]) {
+		_last_group[0] = a;
 		SetDParam(0, a->index);
 		GetString(last_name[0], STR_GROUP_NAME, lastof(last_name[0]));
 	}
 
-	if (b != last_group[1]) {
-		last_group[1] = b;
+	if (b != _last_group[1]) {
+		_last_group[1] = b;
 		SetDParam(0, b->index);
 		GetString(last_name[1], STR_GROUP_NAME, lastof(last_name[1]));
 	}
@@ -207,6 +209,10 @@ private:
 		this->SetWidgetDisabledState(WID_GL_COLLAPSE_ALL_GROUPS, !enable_collapse_all);
 
 		list.ForceResort();
+
+		/* invalidate cached values for name sorter - group names could change */
+		_last_group[0] = _last_group[1] = nullptr;
+
 		list.Sort(&GroupNameSorter);
 
 		AddChildren(&list, INVALID_GROUP, 0);