Only destroy dinput if non-NULL.

input/dinput.c

@@ -475,6 +475,7 @@ bool dinput_handle_message(void *dinput, UINT message, WPARAM wParam, LPARAM lPa
       }
       case WM_DEVICECHANGE:
       {
+         if (di->joypad)
             di->joypad->destroy();
          di->joypad = input_joypad_init_driver(g_settings.input.joypad_driver);
          break;
@@ -491,6 +492,7 @@ static void dinput_free(void *data)
    if (di)
    {
       g_ctx = NULL; // Prevent a joypad driver to kill our context prematurely.
+      if (di->joypad)
          di->joypad->destroy();
       g_ctx = hold_ctx;