[BUGFIX] requestUpdate sensitive to spaces

The TCA property "requestUpdate" is sensitive to spaces, although this
is documented nowhere. Indeed "foo1, foo2" will not work whereas
"foo1,foo2" does. This patch strips spaces from the "requestUpdate"
string before testing it.

Change-Id: Ifbb1fe5be59077207316e48204d65a978592f878
Resolves: #49872
Related: #42789
Releases: 6.2, 6.1, 6.0, 4.7, 4.5
Reviewed-on: https://review.typo3.org/22313
Reviewed-by: Markus Klein
Tested-by: Markus Klein