dbug: avoid printing nothing at all
Previously, if filtering subscriptions turned up no results, nothing was
printed. With this change, we explicitly print "no matching subscriptions"
instead.
(ream grab.dbug)
::
%incoming
+ =; =tang
+ ?^ tang tang
+ [%leaf "no matching subscriptions"]~
%+ murn
%+ sort ~(tap by sup.bowl)
|= [[* a=[=ship =path]] [* b=[=ship =path]]]
==
::
%outgoing
+ =; =tang
+ ?^ tang tang
+ [%leaf "no matching subscriptions"]~
%+ murn
%+ sort ~(tap by wex.bowl)
|= [[[a=wire *] *] [[b=wire *] *]]
