[PATCH] SSI: ensure context of main request exists for subrequest using SSI

[Ciel]

Hello!

Great insights. This version seems way more clear for me, and works perfectly on
my server. So this pronounced like the final fix for this ticket. (Sorry about
forgetting adding the reference again)

Since it may take significant time for the patch to rollout, I'd reachout to the
Debian package maintainers for the patching of Debian 11 bullseye, if this patch
is now accepted by NGINX.

Thanks again for your attention and patience.

Ciel