Table disappears when open preference window the second time

[lzhmark]

I built the latest version locally and import the demo plugin into my Zotero, it seems work well. When I open the preference window, I could see the preference table perfectly. However, after closing the preference window and reopen i, I found that the preference table disappear, no matter how many times I reopen the window.

This is what I saw when open the window for the first time:

When I open the preference window for the second time, the table disappears:

[windingwind]

fixed