Add-DestinationToPSModulePath sometimes fails on first init


EDIT: This appears to be an issue in the profile update code.
```
PS D:\MicrosoftMvp> $error[0]
Test-Path: Value cannot be null. (Parameter 'The provided Path argument was null or an empty collection.')

PS D:\MicrosoftMvp> $error[0].ScriptStackTrace
at Add-DestinationToPSModulePath, C:\Users\JGrote\Documents\PowerShell\Modules\ModuleFast\0.2.0\ModuleFast.psm1: line 1708
at Install-ModuleFast, C:\Users\JGrote\Documents\PowerShell\Modules\ModuleFast\0.2.0\ModuleFast.psm1: line 302
at , : line 1
```

Start at Add-DestinationToPSModulePath in ModuleFast.psm1, using the reported line 1708 and the profile update code context. Reproduce the first-initialization path that produces the null-path Test-Path error; done when first initialization completes without that error.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.