[BUGFIX] Always hide the loading spinner of System Information

If the AJAX request that fetches information for the System Information
toolbar item fails for whatever reason, the spinner is now removed.

This may happen when the session times out and the re-login modal is shown
for a longer period.

Resolves: #81984
Releases: master, 8.7
Change-Id: Ibe9566d29d403e64d55fd0f462d452413d863f0a
Reviewed-on: https://review.typo3.org/53604


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Joerg Boesche <typo3@joergboesche.de>
Tested-by: Joerg Boesche <typo3@joergboesche.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>