[TASK] Suppress db call for rootline with uid 0

Page uid 0 has no rootline by definition. The patch adds an
early return to RootlineUtility to suppress some cache->get()
calls. This happens in BE quite often. Additionally, the
SiteFinder does not query RootlineUtility for page uid 0 at
all to save a series of instance creations.

Resolves: #86271
Releases: master
Change-Id: I63c819c6dcd5e5c7a0e226ae16b0ecd6cf391e30
Reviewed-on: https://review.typo3.org/58289


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>