camel_flag_list_copy: Avoid false 'changed' notifications
camel_flag_list_copy: Avoid false 'changed' notifications

The function, as written, returned that the destination list
changed even in cases where both flag lists were empty. This
made for example IMAPx report that each message in a folder
hanged, even there did not change any.

tintou/evolution-data-server,tintou/evolution-data-server,matzipan/evolution-data-server,tintou/evolution-data-server,matzipan/evolution-data-server,matzipan/evolution-data-server,tintou/evolution-data-server,matzipan/evolution-data-server,matzipan/evolution-data-server