Do not raise an error if the program `editorconfig` is not found.

Instead, ignore the hook function.
Set default value of file coding system.

If the value of `end_of_file` is invalid, the file coding system
should be set to `undecided`, not `nil`.
Do not mark the buffer modified after setting the file coding system.

When I open a file, the buffer is always marked modified.  I have to
type C-x C-s before closing the buffer even I just want to view the
file.  This is annoying.

If we need to convert the coding of a file, we can save the file
explicitly.
Merge pull request #4 from dochang/bugfix

Don't mark untouched buffers changed, improved error handling.