Untrusted certificate from LetsEncrypt E1

Versions

• OS: Windows 10
• Gajim version: 1.3.2

Steps to reproduce the problem

1. Connect a server returning a LetsEncrypt certificate issued by "E1". Make sure to return fullchain.pem which contains three certificates issued by E1, X2, X1. So X1 is the anchor. For further LE CA information https://letsencrypt.org/images/isrg-hierarchy.png
2. Connect your account
3. Notice apparition of certificate trust dialog

Remark: I can PM a test server with such a configuration.

Expected behavior

Gajim should trust the certificate because the anchor (X1) is in the trust store (Local computer / Trusted Root Certification Authorities / Certificates / ISGR Root X1)

Actual behavior

Gajim asks the user to manually enforce trust or reject.