Fixes these install errors on Debian caused by failing to check if the file exists before unblinking, and failing to quote a variable that might be undefined.
Setting up ziti-edge-tunnel (0.22.22) ...
unlink: cannot unlink '/opt/openziti/share/ziti-edge-tunnel.service': No such file or directory
/var/lib/dpkg/info/ziti-edge-tunnel.postinst: 109: [: !=: unexpected operator
Fixes these install errors on Debian caused by failing to check if the file exists before unblinking, and failing to quote a variable that might be undefined.