update plugin-utils Lua example script

scripts/s_pluginutils.lua

@@ -8,6 +8,7 @@ function factory () return function ()
 	for r in Session:get_routes():iter() do
 		if (string.match (r:name(), "dru") and r:n_inputs():n_audio() == 1) then
 			local proc = ARDOUR.LuaAPI.new_plugin(Session, "http://gareus.org/oss/lv2/fil4#mono", ARDOUR.PluginType.LV2, "cutbass");
+			assert (not proc:isnil())
 			r:add_processor_by_index(proc, 0, nil, true)
 		end
 	end
@@ -16,9 +17,12 @@ function factory () return function ()
 	-------------------------------------------------------------------------------
 	-- load a plugin preset
 	route = Session:get_remote_nth_route(2)
+	assert (route)
 	-- to 4th plugin (from top), ardour starts counting at zero
 	plugin = route:nth_plugin(3):to_insert():plugin(0)
+	assert (not plugin:isnil())
 	ps = plugin:preset_by_label("cutbass") -- get preset by name
+	assert (ps)
 	print (ps.uri)
 	plugin:load_preset (ps)
 
@@ -27,7 +31,12 @@ function factory () return function ()
 	-- add a LuaProcessor (here "Scope") to all tracks
 	for t in Session:get_tracks():iter() do
 		local pos = 0 -- insert at the top
-		local proc = ARDOUR.LuaAPI.new_luaproc(Session, "Inline Scope");
+
+		-- the following two lines are equivalent
+		--local proc = ARDOUR.LuaAPI.new_luaproc(Session, "a-Inline Scope");
+		local proc = ARDOUR.LuaAPI.new_plugin (Session, "a-Inline Scope", ARDOUR.PluginType.Lua, "");
+		assert (not proc:isnil())
+
 		t:add_processor_by_index(proc, pos, nil, true)
 		-- optionally set some parameters
 		ARDOUR.LuaAPI.set_processor_param (proc, 0, 5) -- timescale 5sec