Creating a Group DM (GDM) with someone who has GDM invitations blocked while already being in a GDM with that user causes a hidden 400 error

Can reproduce CR: Canary Desktop 2026.528.23728, Web 2026.528.231208, Windows 11 10.0.26200 (x64), Electron 41.2.2, Chrome 146.0.7680.188, Node 24.14.1, Locale en-GB