fdroid: don't treat MetaDataException as unknown
fdroid: don't treat MetaDataException as unknown

Up until now, if it was thrown, fdroid would crash with a full stacktrace as
if the program had stopped unexpectedly. Now it just prints the metadata
error, as intended.

f-droid/fdroidserver,f-droid/fdroid-server,f-droid/fdroidserver,f-droid/fdroidserver,f-droid/fdroidserver,fdroidtravis/fdroidserver,fdroidtravis/fdroidserver,fdroidtravis/fdroidserver,f-droid/fdroid-server,f-droid/fdroidserver,f-droid/fdroid-server,fdroidtravis/fdroidserver,f-droid/fdroid-server,f-droid/fdroid-server