Only install git hook if cloned from git. For source tarballs, the `.git/hooks` folder does not exist, so an error is shown when running `autogen.sh`. With this change, the hook is not installed in such cases.
Only install git hook if cloned from git.
For source tarballs, the `.git/hooks` folder does not exist, so an error
is shown when running `autogen.sh`. With this change, the hook is not
installed in such cases.

strukturag/spreed-webrtc,strukturag/spreed-webrtc,theurere/spreed-webrtc,theurere/spreed-webrtc,theurere/spreed-webrtc,strukturag/spreed-webrtc,theurere/spreed-webrtc,theurere/spreed-webrtc,theurere/spreed-webrtc,strukturag/spreed-webrtc,strukturag/spreed-webrtc,strukturag/spreed-webrtc