ALSA: pcm: Check for null pointer of pointer substream before dereferencing it

In the Linux kernel, the following vulnerability has been resolved:

ALSA: pcm: Check for null pointer of pointer substream before dereferencing it

Pointer substream is being dereferenced on the assignment of pointer card

before substream is being null checked with the macro PCM_RUNTIME_CHECK.

Although PCM_RUNTIME_CHECK calls BUG_ON, it still is useful to perform the

the pointer check before card is assigned.