Fix door conveyance node dupe bug

After successfully moving a node, always stop trying
to move that node to another spot, regardless of
whether or not we had any retries to process as a
result.

mods/nc_doors/convey.lua

@@ -69,6 +69,7 @@ local function tryprocess(item, retry)
 					queued[r.key] = true
 				end
 			end
+			return
 		end
 	end
 	for _, t in ipairs(item.try) do