LoginDialog: connect to login outcomes in setup()

It was done in apply() instead, that can be called several times,
leading to accept() being called several times on the same dialog,
breaking all kinds of assumptions and ending up in a crash. Closes #805.

client/logindialog.cpp

@@ -162,6 +162,10 @@ void LoginDialog::setup(const QString& statusMessage)
                 serverEdit->clear();
                 setStatusMessage(message);
             });
+    connect(m_connection.data(), &Connection::connected,
+            this, &Dialog::accept);
+    connect(m_connection.data(), &Connection::loginError,
+            this, &Dialog::applyFailed);
     auto* formLayout = addLayout<QFormLayout>();
     formLayout->addRow(tr("Matrix ID"), userEdit);
     formLayout->addRow(tr("Password"), passwordEdit);
@@ -194,10 +198,6 @@ void LoginDialog::apply()
         url.setScheme("https"); // Qt defaults to http (or even ftp for some)
 
     // Whichever the flow, the two connections are the same
-    connect(m_connection.data(), &Connection::connected,
-            this, &Dialog::accept);
-    connect(m_connection.data(), &Connection::loginError,
-            this, &Dialog::applyFailed);
     if (m_connection->homeserver() == url && !m_connection->loginFlows().empty())
         loginWithBestFlow();
     else if (!url.isValid())