lightbox: Cast zid to an int before looking it up in message_store.
lightbox: Cast zid to an int before looking it up in message_store.

The keys for message_store are since the recent Map migration intended
to be integer message IDs, not strings (and likely were always
intended to be integers; the failure mode may simply have shifted).

This may just be a new bug, but this max also fix #9549; certainly
we'll want to redo any investigation with this fix in place.

Fixes #9549.

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