Fix invalid memory access in headset_get_nrec when hs->slc is NULL

headset_get_nrec might get called when there's no SLC and it should
return the default NREC value in that case which is TRUE.
diff --git a/audio/headset.c b/audio/headset.c
index 17938f7..1d9f8f2 100644
--- a/audio/headset.c
+++ b/audio/headset.c
@@ -2685,6 +2685,9 @@
 {
 	struct headset *hs = dev->headset;
 
+	if (!hs->slc)
+		return TRUE;
+
 	return hs->slc->nrec;
 }