xdgshellwindow: never request clients to resize to a negative size

Doing that can cause clients to crash

BUG: 489983

src/xdgshellwindow.cpp

@@ -691,8 +691,8 @@ XdgSurfaceConfigure *XdgToplevelWindow::sendRoleConfigure() const
 
     QSizeF nextClientSize = moveResizeGeometry().size();
     if (!nextClientSize.isEmpty()) {
-        nextClientSize.rwidth() -= framePadding.width();
-        nextClientSize.rheight() -= framePadding.height();
+        nextClientSize.setWidth(std::max(1.0, nextClientSize.width() - framePadding.width()));
+        nextClientSize.setHeight(std::max(1.0, nextClientSize.height() - framePadding.height()));
     }
 
     if (nextClientSize.isEmpty()) {