Added index NULL check to submit_buffer_data() in case the driver doesn't like a NULL indices pointer.
Added index NULL check to submit_buffer_data() in case the driver doesn't like a NULL indices pointer.

grimfang4/sdl-gpu,ademuri/sdl-gpu,grimfang4/sdl-gpu,grimfang4/sdl-gpu,ademuri/sdl-gpu,ademuri/sdl-gpu,grimfang4/sdl-gpu,ademuri/sdl-gpu