[BUGFIX] LocalDriver needs to respect "is_writeable"

The LocalDriver needs also to respect the flag "is_writeable".
This means: if the flag is not set, no folder/file can be edited/moved...

Fixes: #44370
Releases: 6.0, 6.1

Change-Id: I404ed51c62ab96d9b5eaaf6c0b7b255bdea3538b
Reviewed-on: https://review.typo3.org/18317
Reviewed-by: Helmut Hummel
Tested-by: Helmut Hummel