[BUGFIX] Prevent search upload folder in write protected storages

If a storage is marked as non-writeable there isn't any possibility to
have an upload folder in there. So this storage should be skipped in the
lookup of the default upload folder of an user.

Resolves: #69303
Releases: master, 6.2
Change-Id: If53b5545a6af6aa1d333d48bb0856a5de070fd2d
Reviewed-on: http://review.typo3.org/42864


Reviewed-by: Morton Jonuschat <m.jonuschat@mojocode.de>
Tested-by: Morton Jonuschat <m.jonuschat@mojocode.de>
Reviewed-by: Nicole Cordes <typo3@cordes.co>
Tested-by: Nicole Cordes <typo3@cordes.co>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Frans Saris <franssaris@gmail.com>
Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Reviewed-by: Philipp Gampe <philipp.gampe@typo3.org>
Tested-by: Philipp Gampe <philipp.gampe@typo3.org>