fix assertion if id is -1

app/dockcorona.cpp

@@ -316,6 +316,9 @@ QRegion DockCorona::availableScreenRegion(int id) const
 
 QRect DockCorona::availableScreenRect(int id) const
 {
+    if (!m_screenPool->knownIds().contains(id))
+        return {};
+
     const auto screens = qGuiApp->screens();
     const QScreen *screen{qGuiApp->primaryScreen()};
     QString scrName = m_screenPool->connector(id);