ImageViewer: Fix crash when opening invalid movie

Qt 6 sends the finished signal directly from QMovie::start, so if we
connect QMovie::finished directly to QMovie::start, we end up in
an endless recursion and stack exhaustion.

Use a queued connection, and do not restart a movie if it went
invalid.

Fixes: QTCREATORBUG-26377
Change-Id: I9980615f44d0cf7e92f85c010427bd6b67046949
Reviewed-by: Robert Löhning <robert.loehning@qt.io>
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

src/plugins/imageviewer/imageviewerfile.cpp

@@ -126,7 +126,15 @@ Core::IDocument::OpenResult ImageViewerFile::openImpl(QString *errorString,
         m_type = TypeMovie;
         m_movie = new QMovie(fileName, QByteArray(), this);
         m_movie->setCacheMode(QMovie::CacheAll);
-        connect(m_movie, &QMovie::finished, m_movie, &QMovie::start);
+        connect(
+            m_movie,
+            &QMovie::finished,
+            m_movie,
+            [this] {
+                if (m_movie->isValid())
+                    m_movie->start();
+            },
+            Qt::QueuedConnection);
         connect(m_movie, &QMovie::resized, this, &ImageViewerFile::imageSizeChanged);
         m_movie->start();
         m_isPaused = false; // force update