Comment 3 for bug 1782308

Core Group review at ESS:

We don't like the case of the leading '+', but we would allow a leading '-' to mean "ignore my request for this filter if the filter is not found, and don't print an error on the IOC".

Implementation would probably require adding a dummy filter to dbChannel.c which accepts any filter arguments, but the result should not be added to the list of filters for the channel.