Fixing a bug where no User environment variable for PSModulePath caused an error in Canonicolize-Path

Error shows when installing a PowerShell module into the Global level

Canonicolize-Path : Cannot bind argument to parameter 'Path' because it is an empty string.
At C:\PsGet\PsGet.psm1:947 char:96
+ ... onicolize-Path $_ })   -contains (Canonicolize-Path $Destination)
+                    ~~
    + CategoryInfo          : InvalidData: (:) [Canonicolize-Path], ParameterBindingValidationException
    + FullyQualifiedErrorId : ParameterArgumentValidationErrorEmptyStringNotAllowed,Canonicolize-Path