Mark items with missing full-text cache files as unsynced for full text
Mark items with missing full-text cache files as unsynced for full text

Fixes #954, Full-text content processor tries to process missing cache
files on every idle

gracile-fr/zotero,retorquere/zotero,retorquere/zotero,gracile-fr/zotero,rmzelle/zotero,rmzelle/zotero,gracile-fr/zotero,retorquere/zotero,rmzelle/zotero