unbreak db_notes when given no addresses

git-svn-id: file:///home/svn/framework3/trunk@13233 4d416f70-5f16-0410-b530-b9f4589650da

lib/msf/ui/console/command_dispatcher/db.rb

@@ -705,6 +705,10 @@ class Db
 				end
 
 			end
+			if hostlist.empty?
+				hostlist = nil
+			end
+
 			case mode
 			when :add
 				if types.size != 1