Invalid selection on "Folder merge" and "Document split" does not cancel the action

[HeyMyian]

Reproduce:

• Select a document in the project tree.
• Choose the menu entry "Merge Folder to Document".
• Error window appears: "Element selected in the project tree must be a folder." <-- expected. Click OK.
• The usual window for folder merging appears. <-- unexpected, because the initial action was invalid and there is nothing to do here.

Analogue selecting a folder and wanting to "Split Document to Folder".

Related: When nothing is selected in the project tree and either of these functions are called, no error message appears -- but the window for merging folders / splitting documents appears. There is nothing do to in them.

[vkbo]

Yes, these dialogs have been around for a long time and are a bit clunky in use, and have some usability issues like the one you're pointing out here. I haven't done anything to improve them because when I implement #1002, they will need to be rewritten anyway. I plan to make a new combined split/merge tool after that is implemented.

[vkbo]

Feature #1072 supersedes this, but leaving the ticket open until it is implemented.