Do a check for powershell.exe before running it.

data/templates/scripts/to_powershell.hta.template

@@ -1,4 +1,7 @@
 <script language="VBScript">
-  Set %{var_shell} = CreateObject("Wscript.Shell")
-  %{var_shell}.Run "%{powershell}"
+  Set %{var_shell} = CreateObject("Wscript.Shell") 
+  Set %{var_fso} = CreateObject("Scripting.FileSystemObject")
+  If %{var_fso}.FileExists(%{var_shell}.ExpandEnvironmentStrings("%%PSModulePath%%") + "..\powershell.exe") Then
+    %{var_shell}.Run "%{powershell}"
+  End If
 </script>

lib/msf/util/exe.rb

@@ -1132,6 +1132,7 @@ require 'msf/core/exe/segment_appender'
     # Intialize rig and value names
     rig = Rex::RandomIdentifierGenerator.new()
     rig.init_var(:var_shell)
+    rig.init_var(:var_fso)
 
     hash_sub = rig.to_h
     hash_sub[:powershell] = powershell