Ensure XInitThreads is called before SDL initialization so threaded nvidia optimization works

indra/llwindow/llwindowsdl.cpp

@@ -239,9 +239,12 @@ LLWindowSDL::LLWindowSDL(LLWindowCallbacks* callbacks,
 	  mGamma(1.0f)
 {
 	SDL_SetMainReady();
-
 	SDL_LogSetOutputFunction(&sdlLogOutputFunc, nullptr);
 
+#if LL_X11
+	XInitThreads();
+#endif
+
 	if (SDL_InitSubSystem(SDL_INIT_EVENTS|SDL_INIT_VIDEO|SDL_INIT_GAMECONTROLLER|SDL_INIT_JOYSTICK) != 0)
 	{
 		LL_WARNS() << "Failed to initialize SDL due to error: " << SDL_GetError() << LL_ENDL;