[BUGFIX] Prioritize iconIdentifier over default icon for extbase modules

If ExtensionUtility::registerModule is called with a module
configuration only containing an icon identifier the default icon of
extbase is unset.

Resolves: #80844
Releases: master, 9.5
Change-Id: I879b4fad2c6881fface0d64581c031b6ac7589eb
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/63612


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Susanne Moog <look@susi.dev>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Susanne Moog <look@susi.dev>
Reviewed-by: Benni Mack <benni@typo3.org>