soft_deactivation: Fix buggy error handling.
soft_deactivation: Fix buggy error handling.

There is no such thing as `max()` on the manager object.  We meant
.last().

Introduced in 37189e1f9db828599e98a2d342e2bbdadf8dd9de, so my bug, in
a rare untested code path.

zulip/zulip,rht/zulip,zulip/zulip,timabbott/zulip,shubhamdhama/zulip,brainwane/zulip,hackerkid/zulip,punchagan/zulip,eeshangarg/zulip,shubhamdhama/zulip,timabbott/zulip,rht/zulip,synicalsyntax/zulip,rht/zulip,eeshangarg/zulip,synicalsyntax/zulip,zulip/zulip,shubhamdhama/zulip,timabbott/zulip,zulip/zulip,timabbott/zulip,kou/zulip,eeshangarg/zulip,showell/zulip,showell/zulip,punchagan/zulip,eeshangarg/zulip,hackerkid/zulip,brainwane/zulip,eeshangarg/zulip,hackerkid/zulip,synicalsyntax/zulip,brainwane/zulip,synicalsyntax/zulip,shubhamdhama/zulip,synicalsyntax/zulip,rht/zulip,hackerkid/zulip,showell/zulip,punchagan/zulip,andersk/zulip,showell/zulip,shubhamdhama/zulip,punchagan/zulip,rht/zulip,punchagan/zulip,shubhamdhama/zulip,andersk/zulip,andersk/zulip,showell/zulip,kou/zulip,showell/zulip,timabbott/zulip,kou/zulip,synicalsyntax/zulip,showell/zulip,synicalsyntax/zulip,andersk/zulip,kou/zulip,eeshangarg/zulip,kou/zulip,kou/zulip,timabbott/zulip,zulip/zulip,hackerkid/zulip,brainwane/zulip,timabbott/zulip,kou/zulip,punchagan/zulip,zulip/zulip,brainwane/zulip,hackerkid/zulip,zulip/zulip,brainwane/zulip,eeshangarg/zulip,hackerkid/zulip,shubhamdhama/zulip,brainwane/zulip,andersk/zulip,rht/zulip,andersk/zulip,andersk/zulip,punchagan/zulip,rht/zulip