Lectures: Disable submit button in file upload dialog if no file is uploaded yet

[florian-glombik]

Is your feature request related to a problem?

When testing a feature I did not upload a file in the file upload lecture unit and tried to save it. I first thought that saving would be broken for file upload exercises but realized that I just did not upload a file (which of course does not make much sense for a file upload lecture unit).

However, Artemis could indicate what the actual issue is to be more self explanatory.

Describe the solution you'd like

Disable the save button until a file is uploaded in the "upload lecture unit view".
Display a tooltip that a file has to be uploaded on the disabled button as long as this has not been done, do not display the tooltip anymore when the button is enabled.

Describe alternatives you've considered

No response

Additional context

Saving does not work before uploading a file, there is no indicator for that in the UI.

[laxerhd]

That bothered me too.
I'd like to add that feature, if you don't mind.

[laxerhd]

I also noticed, that there are more cases in which one would like to disable the button.
If you have a valid form and then decide to remove the name, the button remains clickable. In this case, however, the red error field will prompt you to add a name. I will also be adressing this issue.