Fix more GCC 8.1 warnings  1   master

Fix 3 warnings reported by GCC 8.1 of the following type

```src/client/gameui.cpp:191:43: warning: « void* memset(void*, int, size_t) » effacement d'un objet du type non trivial « struct GameUI::Flags »; use assignment or value-initialization instead [-Wclass-memaccess]
  memset(&m_flags, 0, sizeof(GameUI::Flags));
```

src/client/gameui.cpp

@@ -188,7 +188,7 @@ void GameUI::update(const RunStats &stats, Client *client, MapDrawControl *draw_
 
 void GameUI::initFlags()
 {
-	memset(&m_flags, 0, sizeof(GameUI::Flags));
+	m_flags = GameUI::Flags();
 	m_flags.show_chat = true;
 	m_flags.show_hud = true;
 	m_flags.show_debug = g_settings->getBool("show_debug");

src/game.cpp

@@ -1014,7 +1014,8 @@ bool Game::startup(bool *kill,
 	RenderingEngine::get_scene_manager()->getParameters()->
 		setAttribute(scene::OBJ_LOADER_IGNORE_MATERIAL_FILES, true);
 
-	memset(&runData, 0, sizeof(runData));
+	// Reinit runData
+	runData = GameRunData();
 	runData.time_from_last_punch = 10.0;
 	runData.update_wielded_item_trigger = true;
 

src/gui/guiTable.cpp

@@ -334,7 +334,6 @@ void GUITable::setTable(const TableOptions &options,
 
 		// Make template for new cells
 		Cell newcell;
-		memset(&newcell, 0, sizeof newcell);
 		newcell.content_type = columntype;
 		newcell.tooltip_index = tooltip_index;
 		newcell.reported_column = j+1;