Running build.cmd without VS installed shows "Cannot bind argument to parameter 'Path' because it is null."

Not sure if this is projectsystem problem or repo toolset problem, but we used to show a friendly error if you didn't have the right VS installed and you ran build.cmd, now we show:

```
E:\project-system2>build
Cannot bind argument to parameter 'Path' because it is null.
System.Management.Automation.ParameterBindingValidationException: Cannot bind argument to parameter 'Path' because it is null.
at System.Management.Automation.ExceptionHandlingOps.CheckActionPreference(FunctionContext funcContext, Exception exception)
at System.Management.Automation.Interpreter.ActionCallInstruction`2.Run(InterpretedFrame frame)
at System.Management.Automation.Interpreter.EnterTryCatchFinallyInstruction.Run(InterpretedFrame frame)
at System.Management.Automation.Interpreter.EnterTryCatchFinallyInstruction.Run(InterpretedFrame frame)
at LocateVisualStudio, E:\project-system2\build\Build.ps1: line 96
at Build, E:\project-system2\build\Build.ps1: line 104
at , E:\project-system2\build\Build.ps1: line 155
at , : line 1
```

Start with build/Build.ps1, especially LocateVisualStudio at line 96 and the Build entry point at line 104; the stack trace also identifies the invocation around line 155. Run build.cmd without Visual Studio installed and compare the current null-Path failure with the intended friendly missing-Visual-Studio error. Done means the command reports a clear installation or configuration error instead of the PowerShell binding exception.

Written by the indexing model from the issue text.