BuildUserAgent function throws error when OS name is single worded in etc/os-release

[shettyprathik]

Expected Behavior

Should also support single worded PRETTY_NAME="Chainguard" in /etc/os-release. As per this the pretty name may or may not contain a release code name or OS version.

Current Behavior

Currently it only supports if there are multiple words in PRETTY_NAME=Debian GNU/LINUX 12"

Failure Information

System.ArgumentOutOfRangeException because it's not able to find space in OS description here

Vault 1.16.1
Vault C# Client 0.3.0

Steps to Reproduce

1. Update PRETTY_NAME in /etc/os-release to a single worded name (found this issue when I used a dotnet chainguard image where the pretty name is just one word Chainguard)
2. call VaultConfiguration()

Additional Information

Unhandled exception. System.ArgumentOutOfRangeException: length ('-1') must be a non-negative value. (Parameter 'length')
Actual value was -1.
   at System.ArgumentOutOfRangeException.ThrowNegative[T](T value, String paramName)
   at System.ArgumentOutOfRangeException.ThrowIfNegative[T](T value, String paramName)
   at System.String.ThrowSubstringArgumentOutOfRange(Int32 startIndex, Int32 length)
   at System.String.Substring(Int32 startIndex, Int32 length)
   at Vault.Client.VaultConfiguration.BuildUserAgent()
   at Vault.Client.VaultConfiguration..ctor(String basePath, HttpClientHandler httpClientHandler, Nullable`1 timeout, RetryConfiguration retryConfiguration, RateLimitConfiguration rateLimitConfiguration, TLSConfiguration tlsConfiguration)
   at VaultAdapter..ctor(IOptions`1 options)