Make Install-PowerShellRemoting.ps1 handle empty string in PowerShellHome parameter (PowerShell#10526)

When PowerShellHome is not specified as a runtime parameter to Install-PowerShellRemoting.ps1, the check '-ne $null' is actually an empty string.  Properly checking with [String]::IsNullOrEmpty() solves the problem.

Author: Orca88

src/powershell-native/Install-PowerShellRemoting.ps1

@@ -123,8 +123,8 @@ function Install-PluginEndpoint {
     # Install the plugin #
     #                    #
     ######################
-
-    if ($PowerShellHome -ne $null)
+    
+    if (-not [String]::IsNullOrEmpty($PowerShellHome))
     {
         $targetPsHome = $PowerShellHome
         $targetPsVersion = & "$targetPsHome\pwsh" -NoProfile -Command '$PSVersionTable.PSVersion.ToString()'