Fix case when result is None.
Fix case when result is None.

Which can happen when server returns an error. Close #128.

autozimu/LanguageClient-neovim,autozimu/LanguageClient-neovim,autozimu/LanguageClient-neovim,autozimu/LanguageClient-neovim,autozimu/LanguageClient-neovim,autozimu/LanguageClient-neovim,autozimu/LanguageClient-neovim,autozimu/LanguageClient-neovim,autozimu/LanguageClient-neovim,autozimu/LanguageClient-neovim,autozimu/LanguageClient-neovim,autozimu/LanguageClient-neovim