Switch to WinForms for clipboard

Some windows skus don't have WPF but do include winforms, so switch to winforms to access the clipboard.

Author: lzybkr

PSReadLine/KillYank.cs

@@ -6,7 +6,7 @@
 using System.Collections.Generic;
 using System.Diagnostics.CodeAnalysis;
 using System.Management.Automation.Language;
-using System.Windows;
+using System.Windows.Forms;
 
 namespace Microsoft.PowerShell
 {
@@ -517,7 +517,10 @@ public static void Copy(ConsoleKeyInfo? key = null, object arg = null)
             {
                 textToSet = _singleton._buffer.ToString(); 
             }
-            ExecuteOnSTAThread(() => Clipboard.SetText(textToSet));
+            if (!string.IsNullOrEmpty(textToSet))
+            {
+                ExecuteOnSTAThread(() => Clipboard.SetText(textToSet));
+            }
         }
 
         /// <summary>

PSReadLine/PSReadLine.csproj

@@ -35,13 +35,13 @@
     <Prefer32Bit>false</Prefer32Bit>
   </PropertyGroup>
   <ItemGroup>
-    <Reference Include="PresentationCore" />
     <Reference Include="System" />
     <Reference Include="System.Core" />
     <Reference Include="System.Management.Automation, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=MSIL">
       <SpecificVersion>False</SpecificVersion>
       <HintPath>C:\Program Files (x86)\Reference Assemblies\Microsoft\WindowsPowerShell\3.0\System.Management.Automation.dll</HintPath>
     </Reference>
+    <Reference Include="System.Windows.Forms" />
     <Reference Include="System.Xml.Linq" />
     <Reference Include="System.Data.DataSetExtensions" />
     <Reference Include="Microsoft.CSharp" />

PSReadLine/ScreenCapture.cs

@@ -5,7 +5,7 @@
 using System;
 using System.Diagnostics.CodeAnalysis;
 using System.Text;
-using System.Windows;
+using System.Windows.Forms;
 
 namespace Microsoft.PowerShell
 {