Display gallery loading and failure placeholders in the image viewer

tools/chatgui/src/imageviewer_window.cpp

@@ -131,7 +131,8 @@ void ImageViewerWindow::paintEvent(QPaintEvent*) {
 
     if (m_image.isNull()) {
         p.setPen(QColor(150, 150, 150));
-        p.drawText(rect(), Qt::AlignCenter, QCoreApplication::translate("ChatGui", "Failed to load photo"));
+        p.drawText(rect(), Qt::AlignCenter, m_placeholder.isEmpty() ?
+            QCoreApplication::translate("ChatGui", "Failed to load photo") : m_placeholder);
         return;
     }