event/BufferedSocket: OnSocketReady() returns true after close

Fixes use-after-free bug (https://bugs.musicpd.org/view.php?id=4548).

src/event/BufferedSocket.cxx

@@ -118,9 +118,15 @@ BufferedSocket::OnSocketReady(unsigned flags)
 	if (flags & READ) {
 		assert(!input.IsFull());
 
-		if (!ReadToBuffer() || !ResumeInput())
+		if (!ReadToBuffer())
 			return false;
 
+		if (!ResumeInput())
+			/* we must return "true" here or
+			   SocketMonitor::Dispatch() will call
+			   Cancel() on a freed object */
+			return true;
+
 		if (!input.IsFull())
 			ScheduleRead();
 	}