user_groups: Convert user_group_by_id_dict from Dict to IntDict.
user_groups: Convert user_group_by_id_dict from Dict to IntDict.

Signed-off-by: Anders Kaseorg <dfdb7392591db597bc41cf266a9c3bc12a2706e5@zulipchat.com>

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