[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.

Resolves: #42789
Releases: 6.2, 6.1, 6.0, 4.7, 4.5
Change-Id: I340090e93e7b8645493f8db0c8c374cb1227f684
Reviewed-on: https://review.typo3.org/22174
Reviewed-by: Xavier Perseguers
Tested-by: Xavier Perseguers
Reviewed-by: Stefan Neufeind
Tested-by: Stefan Neufeind
Reviewed-by: Francois Suter
Tested-by: Francois Suter