Fix share permission checkboxes enabled when permissions can not be set

A sharee can reshare a file and set the edit, create, delete and share
permissions of the reshare only if the received share has edit, create,
delete and share permissions, or if they were revoked in the received
share after being set in the reshare. Therefore, the permission
checkboxes in the share menu should be enabled only if the user can set
them (otherwise trying to check them will lead to an error).

Note that "sharePermissions" has all the permissions if the file is not
a reshare but a file owned by the user.

Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>