PowerToys.MonacoPreviewHandler crashes when rendering UTF-8 BOM (#39381)

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- [ ] **Closes:** https://github.com/microsoft/PowerToys/issues/35258
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src/modules/previewpane/MonacoPreviewHandler/MonacoPreviewHandlerControl.cs

@@ -389,7 +389,7 @@ namespace Microsoft.PowerToys.PreviewHandler.Monaco
                 }
 
                 fileReader.Close();
-                _base64FileCode = Convert.ToBase64String(System.Text.Encoding.UTF8.GetBytes(fileContent));
+                _base64FileCode = Convert.ToBase64String(encodingToUse.GetBytes(fileContent));
                 Logger.LogInfo("Reading requested file ended");
             }