R：循环以检查文件是否存在并将其带到列表#fail

I have 735 folders and some of them will have a .grd file inside, others won't. After a lot of research here in stack, I came up with a code to check if the .grd file exists and, if it does, read the .grd into a list, if doesn't, skip it. But it isn't working... the code is resulting in a list with 735 objects, some of thm, empty. This is my code: I have 735 folders and some of them will have a