DEBUG: stream: Add a BUG_ON to never exit process_stream with an expired task

We must never exit for the stream processing function with an expired
task. Otherwise, we are pretty sure this will ends with a spinning loop. It
is really better to abort as far as possible and with the original buggy
state. This will ease the debug sessions.

src/stream.c

@@ -2579,6 +2579,8 @@ struct task *process_stream(struct task *t, void *context, unsigned int state)
 
 		t->expire = tick_first(t->expire, s->conn_exp);
 
+		BUG_ON(tick_is_expired(t->expire, now_ms));
+
 		s->pending_events &= ~(TASK_WOKEN_TIMER | TASK_WOKEN_RES);
 		stream_release_buffers(s);