Show an error when field JSON is corrupt and allow user to re-select.
Show an error when field JSON is corrupt and allow user to re-select.

closes #1489, Show a more intelligible error for corrupted fields


LinuxMercedes/zotero,fbennett/zotero,retorquere/zotero,aurimasv/zotero,retorquere/zotero,egh/zotero,gracile-fr/zotero,adunning/zotero,sendecomp/zotero,egh/zotero,robamler/zotero,robamler/zotero,LinuxMercedes/zotero,adunning/zotero,robamler/zotero,retorquere/zotero,hoehnp/zotero,hoehnp/zotero,adunning/zotero,gracile-fr/zotero,gracile-fr/zotero,sendecomp/zotero,rmzelle/zotero,LinuxMercedes/zotero,egh/zotero,rmzelle/zotero,rmzelle/zotero,sendecomp/zotero,hoehnp/zotero