util: add isConnected() in signal::Connection and signal::ScopedConnection

Change-Id: Iddf2a084ccf137a691cd85c54003182acf0e5afd
Refs: #2308
diff --git a/src/util/signal-scoped-connection.cpp b/src/util/signal-scoped-connection.cpp
index ae90c5f..a0f2d1c 100644
--- a/src/util/signal-scoped-connection.cpp
+++ b/src/util/signal-scoped-connection.cpp
@@ -61,6 +61,12 @@
   m_connection.disconnect();
 }
 
+bool
+ScopedConnection::isConnected() const
+{
+  return m_connection.isConnected();
+}
+
 void
 ScopedConnection::release()
 {