message_list_view: Fix handling of links to deleted streams.
message_list_view: Fix handling of links to deleted streams.

Previously, links to deleted streams would be incorrectly rendered as
stream's name).

Fixes an issue that was reported where after deleting the "general"
stream, the welcome turtle messages might appear as links to

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