previewrenderer: disconnect signals on destroy

also fix some build warnings

Change-Id: Ibbf2e28cb64800e65b8712c6d733aea9aa69c916
GitLab: #356

src/previewrenderer.cpp

@@ -117,13 +117,16 @@ PhotoboothPreviewRender::PhotoboothPreviewRender(QQuickItem* parent)
 {
     connect(this, &PreviewRenderer::lrcInstanceChanged, [this] {
         if (lrcInstance_)
-            connect(lrcInstance_->renderer(), &RenderManager::previewRenderingStopped, [this]() {
-                Q_EMIT hideBooth();
-            });
+            rendererStoppedConnection_ = connect(lrcInstance_->renderer(),
+                                                 &RenderManager::previewRenderingStopped,
+                                                 [this]() { Q_EMIT hideBooth(); });
     });
 }
 
-PhotoboothPreviewRender::~PhotoboothPreviewRender() {}
+PhotoboothPreviewRender::~PhotoboothPreviewRender()
+{
+    disconnect(rendererStoppedConnection_);
+}
 
 QString
 PhotoboothPreviewRender::takePhoto(int size)
@@ -133,6 +136,7 @@ PhotoboothPreviewRender::takePhoto(int size)
             previewImage->copy()
                 .scaled(size, size, Qt::KeepAspectRatioByExpanding, Qt::SmoothTransformation)));
     }
+    return {};
 }
 
 void

src/previewrenderer.h

@@ -82,4 +82,6 @@ Q_SIGNALS:
 
 private:
     void paint(QPainter* painter) override final;
+
+    QMetaObject::Connection rendererStoppedConnection_;
 };