volume listener: check for correct effect descriptor when releasing

It is possible that the effect descriptor in the listener
context is NULL. Attempting to access its fields would result
in a SIGSEGV. Add a check to avoid crashing.

Bug: 63780779
Test: HAL should not be crashing in vol_prc_lib_release
Change-Id: I241890840acab56e0c706ffca542fa2b1ffef02a
diff --git a/post_proc/volume_listener.c b/post_proc/volume_listener.c
index 54226b7..d4aa79f 100644
--- a/post_proc/volume_listener.c
+++ b/post_proc/volume_listener.c
@@ -766,6 +766,16 @@
     pthread_mutex_lock(&vol_listner_init_lock);
     session_id = recv_contex->session_id;
     stream_type = recv_contex->stream_type;
+
+    if (recv_contex->desc == NULL) {
+        ALOGE("%s: Got NULL descriptor, session %u, stream type %u",
+                __func__, session_id, stream_type);
+        if (dumping_enabled) {
+            dump_list_l();
+        }
+        pthread_mutex_unlock(&vol_listner_init_lock);
+        return status;
+    }
     uuid = recv_contex->desc->uuid;
 
     // check if the handle/context provided is valid