Click the "Edit" button on the proxy plug-in selector edit page, and errors are often reported

[lianjunwei]

Click the "Edit" button on the proxy plug-in selector edit page, and errors are often reported. The recurrence probability is more than 50%. If you want to add an upstream, click "Edit" before saving, and the recurrence probability is 100%.

[VampireAchao]

Cannot reproduce the blank screen issue. Maybe this PR can fix the problem?
#534