import script: Fix upload links.
import script: Fix upload links.

Rendered content is None for Slack imports, hence it is replaced only
for Zulip->Zulip imports.

Fixes #8959.

zulip/zulip,andersk/zulip,showell/zulip,brainwane/zulip,andersk/zulip,punchagan/zulip,zulip/zulip,tommyip/zulip,brainwane/zulip,synicalsyntax/zulip,kou/zulip,andersk/zulip,kou/zulip,dhcrzf/zulip,shubhamdhama/zulip,jackrzhang/zulip,synicalsyntax/zulip,brainwane/zulip,tommyip/zulip,showell/zulip,punchagan/zulip,eeshangarg/zulip,rht/zulip,dhcrzf/zulip,hackerkid/zulip,zulip/zulip,shubhamdhama/zulip,rht/zulip,rishig/zulip,showell/zulip,synicalsyntax/zulip,dhcrzf/zulip,rht/zulip,jackrzhang/zulip,brainwane/zulip,hackerkid/zulip,jackrzhang/zulip,jackrzhang/zulip,timabbott/zulip,synicalsyntax/zulip,tommyip/zulip,rht/zulip,synicalsyntax/zulip,tommyip/zulip,zulip/zulip,dhcrzf/zulip,rht/zulip,eeshangarg/zulip,shubhamdhama/zulip,eeshangarg/zulip,zulip/zulip,eeshangarg/zulip,andersk/zulip,showell/zulip,punchagan/zulip,brainwane/zulip,shubhamdhama/zulip,rishig/zulip,shubhamdhama/zulip,punchagan/zulip,andersk/zulip,jackrzhang/zulip,punchagan/zulip,andersk/zulip,rishig/zulip,shubhamdhama/zulip,jackrzhang/zulip,tommyip/zulip,eeshangarg/zulip,jackrzhang/zulip,rishig/zulip,dhcrzf/zulip,kou/zulip,kou/zulip,timabbott/zulip,hackerkid/zulip,synicalsyntax/zulip,dhcrzf/zulip,rishig/zulip,rht/zulip,showell/zulip,rishig/zulip,rht/zulip,hackerkid/zulip,tommyip/zulip,rishig/zulip,punchagan/zulip,dhcrzf/zulip,timabbott/zulip,eeshangarg/zulip,hackerkid/zulip,timabbott/zulip,timabbott/zulip,zulip/zulip,punchagan/zulip,showell/zulip,hackerkid/zulip,shubhamdhama/zulip,showell/zulip,zulip/zulip,brainwane/zulip,kou/zulip,brainwane/zulip,andersk/zulip,kou/zulip,synicalsyntax/zulip,eeshangarg/zulip,timabbott/zulip,tommyip/zulip,kou/zulip,hackerkid/zulip,timabbott/zulip