audio/media: Fix return NULL to .get_name

Player need to have a name set otherwise it may cause the following
crash:

Invalid read of size 1
   at 0x4826BD8: strlen (mc_replace_strmem.c:404)
   by 0x138289: avrcp_handle_get_folder_items (in /usr/libexec/bluetooth/bluetoothd)
   by 0x13A278: handle_browsing_pdu (in /usr/libexec/bluetooth/bluetoothd)
   by 0x1315F2: session_browsing_cb (in /usr/libexec/bluetooth/bluetoothd)
   by 0x48C69BB: g_io_unix_dispatch (in /usr/lib/libglib-2.0.so.0.3600.0)
   by 0x487FB2A: g_main_context_dispatch (in /usr/lib/libglib-2.0.so.0.3600.0)
   by 0x487FEB7: g_main_context_iterate.clone.5 (in /usr/lib/libglib-2.0.so.0.3600.0)
   by 0x48803AA: g_main_loop_run (in /usr/lib/libglib-2.0.so.0.3600.0)
   by 0x16D008: main (in /usr/libexec/bluetooth/bluetoothd)
 Address 0x0 is not stack'd, malloc'd or (recently) free'd
1 file changed