Improve filegroup handling

Author: BartChris

Kitodo/src/main/java/org/kitodo/production/forms/ProjectEditView.java

@@ -70,7 +70,7 @@ public class ProjectEditView extends BaseEditView {
     private boolean locked = true;
     private static final String TITLE_USED = "projectTitleAlreadyInUse";
     private Boolean hasProcesses;
-
+    private String originalFileGroup;
     private Project baseProject;
     /**
      * The folder currently under edit in the pop-up dialog.
@@ -123,6 +123,7 @@ public Folder getEditingFolder() {
      */
     public void setEditingFolder(Folder folder) {
         this.editingFolder = folder;
+        this.originalFileGroup = Objects.nonNull(folder) ? folder.getFileGroup() : null;
         this.generator = new FolderGenerator(folder);
     }
 
@@ -282,6 +283,7 @@ public void saveFolder() {
                         && Objects.equals(folder.getFileGroup(), editingFolder.getFileGroup()));
         if (duplicate) {
             Helper.setErrorMessage("errorDuplicateFilegroup", new Object[] {ObjectType.FOLDER.getTranslationPlural()});
+            editingFolder.setFileGroup(originalFileGroup);
             return;
         }