Save the last floating geometry right before docking

Previously it was only saved on close(), which isn't enough

src/private/DropArea.cpp

@@ -103,6 +103,11 @@ void DropArea::addDockWidget(DockWidgetBase *dw, Location location, DockWidgetBa
     Frame *frame = nullptr;
     Frame *relativeToFrame = relativeTo ? relativeTo->frame() : nullptr;
 
+    if (dw->isFloating()) {
+        // It's getting docked, save last floating position
+        dw->lastPositions().setLastFloatingGeometry(dw->window()->geometry());
+    }
+
     // Check if the dock widget already exists in the layout
     if (contains(dw)) {
         Frame *oldFrame = dw->frame();