Cant add project widget bilder to a pre v0.39-project, which already uses custom widgets

[JojoMueller]

When I try to open a project file, built with pygubu-designer < v0.39, which holds user defined widgets, an error message is displayed: "Class 'customwidgets.cbxxtreeview' not mapped'". Ok. But unfortunately now, changing project settings is impossible: "Open a project first". Pygubu-designer is in a somehow inconsistent state. The widget tree of the project, I tried to open, is displayed, but windows title is still "Pygubu designer - newproject (*)"

Expected behavior
I think it would be best in this case, to load the project despite of this error, and to open the project settings dialog.

Environment

• Windows 10
• Python 3.12
• pygubu 0.35.1
• pygubu-designer 0.39.2

As a workaround, manually editing the ui file should not be too difficult.