lua-factory: Fix performer key containing only one name
lua-factory: Fix performer key containing only one name

Fix the handling of arrays of strings. We shouldn't always overwrite the
names previously there, especially as the key is emptied before handling
tables of values.

https://bugzilla.gnome.org/show_bug.cgi?id=752681

jasuarez/grilo-plugins,MikePetullo/grilo-plugins,MikePetullo/grilo-plugins,GNOME/grilo-plugins,grilofw/grilo-plugins,GNOME/grilo-plugins,jasuarez/grilo-plugins,grilofw/grilo-plugins,MikePetullo/grilo-plugins