A quick xhtml-only fix for the "template with custom terms of use" bug

[landreev]

What this PR does / why we need it:

This fixes, or works around the bug by disabling everything inside the file-download-popup-fragment when the page is in CREATE mode.

Which issue(s) this PR closes:

Closes #9825

Special notes for your reviewer:

Going forward, we may want to consider adding some null checks inside the java code to prevent this; it's not entirely impossible that another developer will add some code that will try to call this method on a dataset that doesn't yet have a persistent id for whatever reason - ?

Suggestions on how to test this:

see the linked issue for the steps to reproduce the bug.

edit: would also be prudent to confirm that the file download popup is still working when you are actually downloading files from a dataset that has terms of use. I have tested - but worth confirming.

Does this PR introduce a user interface change? If mockups are available, please link/include them here:

Is there a release notes update needed for this change?:

Additional documentation:

[kcondon]

It does do something weird but likely not related to this bug or fix: if you download a file from the files page with custom terms enabled, it does show the terms download popup and accepting it downloads the file and the popup disappears but there is a copy of the popup in the file preview iframe, also with an accept button you can click, though it doesn't seem to do anything. Weird. I think this fix is good and the other maybe a separate bug?

OK, it appears to be as designed after testing on demo. The file preview is a download of type explore and so is also hidden by custom terms form. The download in this case is the preview. So, this works, merging/closing.