[effects/thumbnailaside] Save shortcuts

Summary:
If user selects a shortcut to trigger the effect, that shortcut won't
work after the KCM is closed because we don't save it.

BUG: 400351
FIXED-IN: 5.14.3

Test Plan:
* Specified custom shortcut to trigger the effect;
* Closed the KCM;
* Pressed the shortcut, a thumbnail appeared.

Reviewers: #kwin, graesslin

Reviewed By: #kwin, graesslin

Subscribers: kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D16456

effects/thumbnailaside/thumbnailaside_config.cpp

@@ -89,6 +89,7 @@ ThumbnailAsideEffectConfig::~ThumbnailAsideEffectConfig()
 void ThumbnailAsideEffectConfig::save()
 {
     KCModule::save();
+    m_ui->editor->save();
     OrgKdeKwinEffectsInterface interface(QStringLiteral("org.kde.KWin"),
                                          QStringLiteral("/Effects"),
                                          QDBusConnection::sessionBus());