[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: #49872
Related: #42789
Releases: 6.2, 6.1, 6.0, 4.7, 4.5
Change-Id: I44410007503443843a3ecbff15f4738cd857b73c
Reviewed-on: https://review.typo3.org/22314
Reviewed-by: Markus Klein
Tested-by: Markus Klein