deoplete-clang can't deal with files open with Netrw

## Problems summary
I recently tried to open a file over the scp:// protocol which is handled by Vim's "Netrw" plugin. When trying to autocomplete a word, the message
```
[deoplete] Traceback (most recent call last):
[deoplete] File "/home/me/.vim/bundle/repos/github.com/Shougo/deoplete.nvim/rplugin/python3/deoplete/deoplete.py", line 100, in gather_results
[deoplete] ctx['candidates'] = source.gather_candidates(ctx)
[deoplete] File "/home/me/.vim/bundle/repos/github.com/zchee/deoplete-clang/rplugin/python3/deoplete/sources/deoplete_clang.py", line 151, in gather_candidates
[deoplete] params)
[deoplete] File "/home/me/.vim/bundle/repos/github.com/zchee/deoplete-clang/rplugin/python3/deoplete/sources/deoplete_clang.py", line 314, in get_completion
[deoplete] tu = self.get_translation_unit(fname, args, buf)
[deoplete] Traceback (most recent call last):
[deoplete] File "/home/me/.vim/bundle/repos/github.com/zchee/deoplete-clang/rplugin/python3/deoplete/sources/deoplete_clang.py", line 302, in get_translation_unit
[deoplete] File "/home/me/.vim/bundle/repos/github.com/Shougo/deoplete.nvim/rplugin/python3/deoplete/deoplete.py", line 100, in gather_results
[deoplete] tu.save(ast_file)
[deoplete] ctx['candidates'] = source.gather_candidates(ctx)
[deoplete] File "/home/me/.vim/bundle/repos/github.com/zchee/deoplete-clang/rplugin/python3/deoplete/clang/clang/cindex.py", line 2638, in save
[deoplete] File "/home/me/.vim/bundle/repos/github.com/zchee/deoplete-clang/rplugin/python3/deoplete/sources/deoplete_clang.py", line 151, in gather_candidates
[deoplete] 'Error saving TranslationUnit.')
[deoplete] params)
[deoplete] clang.cindex.TranslationUnitSaveError: Error 1: Error saving TranslationUnit.
[deoplete] File "/home/me/.vim/bundle/repos/github.com/zchee/deoplete-clang/rplugin/python3/deoplete/sources/deoplete_clang.py", line 314, in get_completion
[deoplete] Could not get completions from: clang. Use :messages for error details.
[deoplete] tu = self.get_translation_unit(fname, args, buf)
[deoplete] File "/home/me/.vim/bundle/repos/github.com/zchee/deoplete-clang/rplugin/python3/deoplete/sources/deoplete_clang.py", line 302, in get_translation_unit
[deoplete] tu.save(ast_file)
[deoplete] File "/home/me/.vim/bundle/repos/github.com/zchee/deoplete-clang/rplugin/python3/deoplete/clang/clang/cindex.py", line 2638, in save
[deoplete] 'Error saving TranslationUnit.')
[deoplete] clang.cindex.TranslationUnitSaveError: Error 1: Error saving TranslationUnit.
[deoplete] Could not get completions from: clang. Use :messages for error details.
```
is shown.

## Expected
No error message and the autocompletion popup is filled as it would be with a local file.

## Environment Information

- OS: Gentoo GNU/Linux 4.4.6
- Neovim version: NVIM v0.2.0-44-g8089292

## Provide a minimal init.vim with less than 50 lines and not plugin manager (Required!)

```vim
set runtimepath+=/tmp/deoplete.nvim/
set runtimepath+=~/tmp/deoplete-clang/
let g:deoplete#enable_at_startup = 1
```

## The reproduce ways from neovim starting (Required!)

1. run nvim -u /tmp/vimrc scp://server/tmp/tmp.c
2. Press a (in order to go into insert mode)
3. press "int". Once the 't' is pressed, the error messages will be shown.

## Upload the log file
Since the log file is very large I uploaded it here: https://gist.github.com/glacambre/bb959fd61acd3385c95e8aa4b5e134d9
There's nothing interesting in my .nvimlog.

I think this is a bug with deoplete-clang because other autocompletion plugins (deoplete-jedi for example) do not have this bug.