Fix CS8604 (possible null dereferencing) warnings

[atifaziz]

This PR addressed the following two CS8604 warnings:

A:\CSnakes\main\src\CSnakes.Runtime\Locators\NuGetLocator.cs(15,102): warning CS8604: Possible null reference argument for parameter 'path1' in 'string Path.Combine(string path1, string path2, string path3)'. [A:\CSnakes\main\src\CSnakes.Runtime\CSnakes.Runtime.csproj]
A:\CSnakes\main\samples\Aspire\CSnakesAspire.ApiService\Program.cs(65,88): warning CS8602: Dereference of a possibly null reference. [A:\CSnakes\main\samples\Aspire\CSnakesAspire.ApiService\CSnakesAspire.ApiService.csproj]

that were being flagged during build and also adding a lot of GH Actions annotation noise in PR diffs:

[tonybaloney]

Thanks!!