Fixes T443
Fixes T443

Summary: Prevent users to access or delete files belonging to an other namespace.

Test Plan: Tested manually

Reviewers: dlitz, emfree

Reviewed By: emfree

Projects: #security

Maniphest Tasks: T443

Differential Revision: https://review.inboxapp.com/D471

EthanBlackburn/sync-engine,gale320/sync-engine,nylas/sync-engine,gale320/sync-engine,nylas/sync-engine,ErinCall/sync-engine,PriviPK/privipk-sync-engine,nylas/sync-engine,closeio/nylas,EthanBlackburn/sync-engine,wakermahmud/sync-engine,EthanBlackburn/sync-engine,EthanBlackburn/sync-engine,nylas/sync-engine,Eagles2F/sync-engine,jobscore/sync-engine,Eagles2F/sync-engine,jobscore/sync-engine,ErinCall/sync-engine,wakermahmud/sync-engine,ErinCall/sync-engine,closeio/nylas,wakermahmud/sync-engine,Eagles2F/sync-engine,PriviPK/privipk-sync-engine,wakermahmud/sync-engine,PriviPK/privipk-sync-engine,closeio/nylas,gale320/sync-engine,jobscore/sync-engine,gale320/sync-engine,wakermahmud/sync-engine,Eagles2F/sync-engine,EthanBlackburn/sync-engine,PriviPK/privipk-sync-engine,Eagles2F/sync-engine,gale320/sync-engine,ErinCall/sync-engine,closeio/nylas,jobscore/sync-engine,ErinCall/sync-engine,PriviPK/privipk-sync-engine