Fix crash when untitled files are opened as PowerShell (#815)

Author: rjmholt

src/PowerShellEditorServices/Workspace/ScriptFile.cs

@@ -648,7 +648,16 @@ private void ParseFileContents()
                     .Select(ScriptFileMarker.FromParseError)
                     .ToArray();
 
-            //Get all dot sourced referenced files and store  them
+            // Untitled files have no directory
+            // Discussed in https://github.com/PowerShell/PowerShellEditorServices/pull/815.
+            // Rather than working hard to enable things for untitled files like a phantom directory,
+            // users should save the file.
+            if (IsUntitledPath(this.FilePath))
+            {
+                return;
+            }
+
+            // Get all dot sourced referenced files and store them
             this.ReferencedFiles = AstOperations.FindDotSourcedIncludes(this.ScriptAst, Path.GetDirectoryName(this.FilePath));
         }