Fix race condition

One process can remove the cached content after we execute is_file() but before we read it. Such scenario results in the app returning a 500 status code and logging an error saying: “file_get_contents(…): failed to open stream: No such file or directory”.

By using file_get_contents directly we can suppress the error (incase of a missing file). We lose the LF conversion, but since we write the cache file content ourself, this should not be an issue.

I removed the is_file() check since with a non-failing version of file_get_contents that check is redundant.