lua reset_mixer script: ignore hidden io processors like "main out"

* fixes a problem in Mixbus where the reset script will kill audio output

share/scripts/reset_mixer.lua

@@ -152,10 +152,12 @@ function factory() return function()
 				if prefs["io"] then
 					local io_proc = proc:to_ioprocessor()
 					if not(io_proc:isnil()) then
+						if insert:is_channelstrip() or not(insert:display_to_user()) then
 							queue[#queue + 1] = proc
 						end
 					end
 				end
+			end
 			i = i + 1
 		until proc:isnil()