Add compatibility with Gnome-Shell < 3.34 on branch pre-45 - RHEL 8 related

[NVieville]

Hello,

I wonder if you could review and, if appropriated apply the pull request made to upstream repository:

paradoxxxzero#790

It's about keeping compatibility with old gnome-shell versions, specially for RHEL 8 actually
used by some users. It would be great to have it in the pre-45 branch of your repository.

As I maintain the Fedora package of this great gnome-shell extension, I'm thinking of
switching the sources of this package to your fork of the historical/upstream repository for
all the packaged versions of this extension. As you applied some pull request coming
from the upstream repository (gnome-shell 44 compatibility for example) to your
pre-45 branch, I wonder if this could be the same for some other pull requests.

Feel free to make any comment about this pull-request/issue (I didn't know how to do it).
Thanks for taking this extension to gnome-shell 45.

Cordially,

--
NVieville