Option to not clear metadata if the lookups don't work

[Maury Markowitz]

The normal first action when using the queue is to clear out any existing metadata. If the file in question does not match on one of the metadata services, this causes the file to be classified as “Home Video”.

It would be nice to have an option to only clear the metadata if it finds it successfully. This is different than the option of clearing or not clearing metadata that we have now, perhaps under it, indented, as “… but only if it can be found” or something to that effect.