linux: (de)initialize d-bus at init and quit.

Previously we had different subsystems quitting it, in conflict, and risked
multiple threads racing to init it at the same time.

Fixes #3643.

src/SDL.c

@@ -34,6 +34,9 @@
 #include "thread/os2/SDL_systls_c.h"
 #endif
 
+/* this checks for HAVE_DBUS_DBUS_H internally. */
+#include "core/linux/SDL_dbus.h"
+
 #if defined(__EMSCRIPTEN__)
 #include <emscripten.h>
 #endif
@@ -155,6 +158,10 @@ SDL_InitSubSystem(Uint32 flags)
     /* Clear the error message */
     SDL_ClearError();
 
+#if SDL_USE_LIBDBUS
+    SDL_DBus_Init();
+#endif
+
     if ((flags & SDL_INIT_GAMECONTROLLER)) {
         /* game controller implies joystick */
         flags |= SDL_INIT_JOYSTICK;
@@ -442,6 +449,10 @@ SDL_Quit(void)
     SDL_AssertionsQuit();
     SDL_LogResetPriorities();
 
+#if SDL_USE_LIBDBUS
+    SDL_DBus_Quit();
+#endif
+
     /* Now that every subsystem has been quit, we reset the subsystem refcount
      * and the list of initialized subsystems.
      */