Fix method UserAgentClientMinorVersion

Fix UserAgentClientMinorVersion. UserAgent may not always have the patchversion. So, need to parse for minor version slightly differently.
Only added comments to function 'UserAgentClientMajorVersion'

Ran the following tests

DECLARE		@UserAgent1 nvarchar(4000) = 'NuGet Command Line/2.8.4 (Microsoft Windows NT 6.3.9600.0)'
DECLARE		@UserAgent2 nvarchar(4000) = 'NuGet Command Line/2.8 '
DECLARE		@UserAgent3 nvarchar(4000) = 'NuGet Command Line/2.8 (Microsoft Windows NT 6.3.9600.0)'
DECLARE		@UserAgent4 nvarchar(4000) = 'NuGet Command Line/2.8'

SELECT		[dbo].[UserAgentClientMinorVersion-Test](@UserAgent1)
SELECT		[dbo].[UserAgentClientMinorVersion-Test](@UserAgent2)
SELECT		[dbo].[UserAgentClientMinorVersion-Test](@UserAgent3)
SELECT		[dbo].[UserAgentClientMinorVersion-Test](@UserAgent4)

SELECT		[dbo].[UserAgentClientMajorVersion-Test](@UserAgent1)
SELECT		[dbo].[UserAgentClientMajorVersion-Test](@UserAgent2)
SELECT		[dbo].[UserAgentClientMajorVersion-Test](@UserAgent3)
SELECT		[dbo].[UserAgentClientMajorVersion-Test](@UserAgent4)
Side note... the case for when this will throw and halt replication is something we need to make sure we're able to see in monitoring. + @zhili1208.