Bug 1033964 - [NFC] Could not share the file which opened via notification

https://bugzilla.mozilla.org/show_bug.cgi?id=1033964
we don't need setNFCSharing set to false here as we are setting NFC sharing true after opening the blob. It will be safer to move setNFCSharing to false inside done when user clicks on back icon, https://github.com/mozilla-b2g/gaia/blob/master/apps/gallery/js/open.js#L215. 
ALso, please check if we need to setNFCSharing to false when open inline activity window is hidden by pressing home button or switching to a different app.