Fix no icon for 3GP files

Commit 6f6094da does not
do what it said. It said
"   We are now defaulting to treating 3GP files as video files for
    determining the default icon as it was parsing the video files for
    their metadata which was causing ANR problems."
However it returns no icon for 3GP.
Fix it to do what it said in that commit.

FEIJ-202 FEIJ-1347

Change-Id: Ieb57583316594c0308792ff8b43aadf1b15d74a5