ALSA: usb-audio: Fix possible NULL dereference at create_yamaha_midi_quirk()

The previous addition of descriptor validation may lead to a NULL
dereference at create_yamaha_midi_quirk() when either injd or outjd is
NULL.  Add proper non-NULL checks.

Fixes: 57f8770620 ("ALSA: usb-audio: More validations of descriptor units")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/quirks.c

@@ -248,8 +248,8 @@ static int create_yamaha_midi_quirk(struct snd_usb_audio *chip,
 					NULL, USB_MS_MIDI_OUT_JACK);
 	if (!injd && !outjd)
 		return -ENODEV;
-	if (!snd_usb_validate_midi_desc(injd) ||
-	    !snd_usb_validate_midi_desc(outjd))
+	if (!(injd && snd_usb_validate_midi_desc(injd)) ||
+	    !(outjd && snd_usb_validate_midi_desc(outjd)))
 		return -ENODEV;
 	if (injd && (injd->bLength < 5 ||
 		     (injd->bJackType != USB_MS_EMBEDDED &&