journald/read: avoid being blocked on send

In case the LogConsumer is gone, the code that sends the message can
stuck forever. Wrap the code in select case, as all other loggers do.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

daemon/logger/journald/read.go

@@ -230,12 +230,17 @@ drain:
 				kv := strings.SplitN(C.GoStringN(data, C.int(length)), "=", 2)
 				attrs = append(attrs, backend.LogAttr{Key: kv[0], Value: kv[1]})
 			}
-			// Send the log message.
-			logWatcher.Msg <- &logger.Message{
+			// Send the log message, unless the consumer is gone
+			select {
+			case <-logWatcher.WatchConsumerGone():
+				done = true // we won't be able to write anything anymore
+				break drain
+			case logWatcher.Msg <- &logger.Message{
 				Line:      line,
 				Source:    source,
 				Timestamp: timestamp.In(time.UTC),
 				Attrs:     attrs,
+			}:
 			}
 		}
 		// If we're at the end of the journal, we're done (for now).