NXP-11352: Fix wrong handling of the '|' separator for the sortInfos param

See https://jira.nuxeo.com/browse/NXP-11352

Assuming this option for the sorting direction never worked, I switched the character to a space, for consistency with operation "Social.Provider" (class SocialProviderOperation).

**EDIT:** If this gets merged, the documentation at http://explorer.nuxeo.org/nuxeo/site/distribution/current/viewOperation/Document.PageProvider will have to be updated. It has to be anyway since the documentation itself has an additional mistake: the actual default sorting direction is the ascending one.