[DRE-maint] Bug#961017: schleuder: x-add-key fails for inline key material followed by non-key material like a signature

[Georg Faerber]

Package: schleuder
Version: 3.5.1-1
Forwarded: https://0xacab.org/schleuder/schleuder/-/issues/470
Control: found -1 3.4.0-2+deb10u3

x-add-key fails for users sending mails with inline key material,
followed by non-key material, for example a signature included in the
body.

A fix was proposed upstream.