Remove ConnectionInfo after socket is destroyed

This leaves the ConnectionInfo in a valid state, even after the socket is disconnected, which could still have a readyRead() signal emitted.

Closes #123

singleapplication_p.cpp

@@ -328,10 +328,12 @@ void SingleApplicationPrivate::slotConnectionEstablished()
         }
     );
 
-    QObject::connect(nextConnSocket, &QLocalSocket::disconnected,
-        [nextConnSocket, this](){
+    QObject::connect(nextConnSocket, &QLocalSocket::disconnected, nextConnSocket, &QLocalSocket::deleteLater);
+
+    QObject::connect(nextConnSocket, &QLocalSocket::destroyed,
+        [nextConnSocket, this](QObject *obj){
+            Q_UNUSED(obj)
             connectionMap.remove(nextConnSocket);
-            nextConnSocket->deleteLater();
         }
     );