Small refactor

Signed-off-by: Rahix <rahix@rahix.de>

bc.lua

@@ -280,8 +280,7 @@ function BaseControl:set(name, value)
       local old = self.local_nouns[name]
       self.local_nouns[name] = value
 
-      if self.listeners[name] ~= nil then
-        for id, l in pairs(self.listeners[name]) do
+      for id, l in pairs(self.listeners[name] or {}) do
         if   (l.query.ty == Query.Change.ty and value ~= old)
           or (l.query.ty == Query.Rising.ty and value > old)
           or (l.query.ty == Query.Falling.ty and value < old)
@@ -302,7 +301,6 @@ function BaseControl:set(name, value)
         end
       end
     end
-    end
   elseif self.local_verbs[name] ~= nil then
     if type(value) ~= "function" then
       error("\""..name.."\" can't be cast into a noun")