Sharesheet - Support sharing from downloads

Don't assume that all shared files have a DISPLAY_NAME index.
Downloads provide a different title index, so check the cursor
index for -1 values. Also make sure to close the cursor when done.

Bug: 124448157
Test: atest ChooserActivityTest, manually test sharing a download
Change-Id: I0beda6b72fb74c65fc4665c8234f147667925784