rs: fix error logs and compilation warning on non-windows

[connor4312]

Fixes #388

Changes proposed:

• Avoids noisy error logging if no access policies are configured
• Fixes a compilation warning, and generate the user agent string in a slightly DRY-er way

Other Tasks:

• If you updated the Go SDK did you update the PackageVersion in tunnels.go
• If you updated the TS SDK did you update the dependencies in package.json for connections and management to require a dependency that is > the current published version(Found using npm view @microsoft/dev-tunnels-contracts). This will fix issues where yarn will pull the old version of packages and will cause mismatched dependencies. See example PR