Restore open/save dialog when cancelling MIME type intercept
Restore open/save dialog when cancelling MIME type intercept

Behavior from #617 apparently got lost in the transition to master

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