Move mod asset validation from BlankLoadScreen.StartGame() to Game.InitializeMod()

This fixes a crash that happens when you try to launch a mod directly while its assets aren't installed.
Additionally should reduce the overhead for dedicated servers (in theory).

OpenRA.Game/Game.cs

@@ -281,14 +281,30 @@ namespace OpenRA
 			Sound.Initialize();
 
 			ModData = new ModData(mod, !Settings.Server.Dedicated);
-			ModData.MountFiles();
-			ModData.InitializeLoaders();
-			if (!Settings.Server.Dedicated)
-				Renderer.InitializeFonts(ModData.Manifest);
 
 			using (new PerfTimer("LoadMaps"))
 				ModData.MapCache.LoadMaps();
 
+			if (Settings.Server.Dedicated)
+			{
+				RunDedicatedServer();
+				Environment.Exit(0);
+			}
+
+			var installData = ModData.Manifest.Get<ContentInstaller>();
+			var isModContentInstalled = installData.TestFiles.All(f => File.Exists(Platform.ResolvePath(f)));
+
+			// Mod assets are missing!
+			if (!isModContentInstalled)
+			{
+				InitializeMod("modchooser", new Arguments());
+				return;
+			}
+
+			ModData.MountFiles();
+			ModData.InitializeLoaders();
+			Renderer.InitializeFonts(ModData.Manifest);
+
 			if (Cursor != null)
 				Cursor.Dispose();
 
@@ -320,13 +336,17 @@ namespace OpenRA
 
 			JoinLocal();
 
-			if (Settings.Server.Dedicated)
+			ModData.LoadScreen.StartGame(args);
+		}
+
+		public static void RunDedicatedServer()
 		{
 			while (true)
 			{
 				Settings.Server.Map = WidgetUtils.ChooseInitialMap(Settings.Server.Map);
 				Settings.Save();
 				CreateServer(new ServerSettings(Settings.Server));
+
 				while (true)
 				{
 					Thread.Sleep(100);
@@ -348,11 +368,6 @@ namespace OpenRA
 
 				break;
 			}
-
-				Environment.Exit(0);
-			}
-			else
-				ModData.LoadScreen.StartGame(args);
 		}
 
 		public static void LoadEditor(string mapUid)

OpenRA.Mods.Common/LoadScreens/BlankLoadScreen.cs

@@ -41,16 +41,6 @@ namespace OpenRA.Mods.Common.LoadScreens
 			Ui.ResetAll();
 			Game.Settings.Save();
 
-			var installData = Game.ModData.Manifest.Get<ContentInstaller>();
-			var isModContentInstalled = installData.TestFiles.All(f => GlobalFileSystem.Exists(Path.GetFileName(f)));
-
-			// Mod assets are missing!
-			if (!isModContentInstalled)
-			{
-				Game.InitializeMod("modchooser", new Arguments());
-				return;
-			}
-
 			// Join a server directly
 			var connect = Launch.GetConnectAddress();
 			if (!string.IsNullOrEmpty(connect))