[BUGFIX] Do not render empty title attributes in ImageViewHelper

The ImageViewHelper uses strict types for checking if
the `title` property of the image is not an empty string.
Since this value can also be NULL, a typecast is necessary
for the check to work.

Resolves: #91759
Releases: master, 10.4
Change-Id: Ide73a6d2aacf0fcd9bb4c6128a66b0685d4fc68c
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/67504


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Jochen <rothjochen@gmail.com>
Tested-by: Daniel Goerz <daniel.goerz@posteo.de>
Reviewed-by: Jochen <rothjochen@gmail.com>
Reviewed-by: Daniel Goerz <daniel.goerz@posteo.de>