Create .bak file when loading fails (#3984)

* Create backup on file loading fail

When loading a file that has errors in it, Bloxstrap would previously overwrite the file with the defaults. This commit now copies the file to a .bak file with the same name so the user can choose to edit it and fix issues.

* Overwrite backup and handle exceptions

Bloxstrap/JsonManager.cs

@@ -47,6 +47,17 @@ public virtual void Load(bool alertFailure = true)
 
                     if (!String.IsNullOrEmpty(message))
                         Frontend.ShowMessageBox($"{message}\n\n{ex.Message}", System.Windows.MessageBoxImage.Warning);
+
+                    try
+                    {
+                        // Create a backup of loaded file
+                        File.Copy(FileLocation, FileLocation + ".bak", true);
+                    }
+                    catch (Exception copyEx)
+                    {
+                        App.Logger.WriteLine(LOG_IDENT, $"Failed to create backup file: {FileLocation}.bak");
+                        App.Logger.WriteException(LOG_IDENT, copyEx);
+                    }
                 }
 
                 Save();