shell/cat_file:Fix cat not outputting file with no newline at end

Summary

The phenomenon is that when I create a file, such as 123.txt, in the root directory using the edit command, and type some content without pressing Enter to add a newline at the end, upon saving with F9, I can see the file 123.txt exists when using the ls command. However, when I try to view the content with the cat command, nothing is output.