[BUGFIX] Cast string to float in NumberViewHelper

While number_format does an internal cast to float, it does not cast
things like empty strings to 0 - instead a PHP warning is emitted.

To catch that edge case, we are now casting to float before calling
number_format.

Resolves: #90786
Releases: master, 9.5
Change-Id: Ibfbacd2606dabd926adc140960e1116076bbdb5f
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/63798


Tested-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Guido Schmechel <guido.schmechel@brandung.de>
Reviewed-by: Benni Mack <benni@typo3.org>