QWaylandWindow::attach(buffer,x,y) crash if asserts enabled and buffer==nullptr

diff --git a/src/client/qwaylandwindow.cpp b/src/client/qwaylandwindow.cpp
index 05fc7d88..cf116936 100644
--- a/src/client/qwaylandwindow.cpp
+++ b/src/client/qwaylandwindow.cpp
@@ -579,8 +579,8 @@ void QWaylandWindow::handleScreenRemoved(QScreen *qScreen)
 
 void QWaylandWindow::attach(QWaylandBuffer *buffer, int x, int y)
 {
-    Q_ASSERT(!buffer->committed());
-    if (buffer) {
+   if (buffer) {
+        Q_ASSERT(!buffer->committed());
         handleUpdate();
         buffer->setBusy();