Mass creation of categories fails weirdly if a categoruy already exists

[nomike]

Describe the bug
If I'm trying to mass create a category where one of the parents already exists, an error occurs in a weird way which doesn´t go away until you refresh the browser.

To Reproduce
Steps to reproduce the behavior:

1. Go to 'Edit' → 'Categories'
2. Click on 'New Element'
3. Go to the 'Mass creation' tab
4. Enter the following text to create new categories:

Prototyping, Fabrication Products
  Solderless Breadboards

5. Click on "Create"
6. Click on 'New Element' again.
7. Enter the following:

Prototyping, Fabrication Products
  Jumper Wire

8. Click on "Create"

Actual behavior
Instead of the behavior mentioned above an error is thrown and a HTTP/500 is shown in the background of the page, behind all other controls and forms.

The page looked like this, directly before clicking "Create" in step 8.:

And looks like this immediately after clicking:

Some text is white on white background which can be revealed by selecting it:

This error doesn't go away regardless of where you browse to in Part-DB. Only a browser refresh gets rid of it.

Expected behavior
I would expect Part-DB to create a new category named 'Jumper Wire" which is a descendant of the already existing category named "Prototyping, Fabrication Products". As this category already exists, it should be silently ignored.

If all categories specified already exist, I would also expect this to be silently ignored.

What I as a user want is for the specified categories to exist once I've clicked "Create", whether they already existed before that, I don´t care.

And even if this is not an option, if should at least show a user-friendly error message.

Screenshots
See above.

Server Side

• Part-DB Version: v.11.1.1
• PHP Version: 8.2.7
• Database Server: sqlit 3.40.1

Desktop (please complete the following information):

• OS: Ubuntu 23.10
• Browser: Firefox
• Version: 123.0 (64-bit)

[jbtronics]

This should be fixed with the latest commit.