fix: Handle empty fileencoding by falling back to global encoding

[Syu-fu]

Description

This fix addresses an issue where an error occurs if the buffer's fileencoding option is empty during certain operations, such as applying text edits in the LSP. (#344)

Context

While similar issues regarding file encodings have been reported and resolved, this specific case occurs when the fileencoding of a buffer is not explicitly set. In such cases, the empty string ("") is returned, leading to failures in functions that expect a valid encoding (e.g., vim.lsp.util.apply_text_edits).

Changes

• Added a fallback mechanism to use the global encoding option (vim.o.encoding) if fileencoding is empty.
• Ensured that the user’s configuration for encoding is respected before defaulting to "utf-8".

Steps to Reproduce

1. Open a new file in Neovim (e.g., nvim newfile.txt).
2. Without saving the file or setting fileencoding, trigger an operation that depends on the file's encoding, such as applying LSP edits.
3. Observe the error due to the empty fileencoding.

Fix Explanation

The fix retrieves the fileencoding value for the buffer and checks if it is empty. If it is, the global encoding setting is used as a fallback. This ensures that the operation continues with a valid encoding, avoiding errors.

[fserb]

Thanks so much for this. I've been getting those errors and have to force set encoding a lot.

[unlimitedsola]

I personally find this easier to read.

Suggested change

	local encoding = vim.api.nvim_get_option_value("fileencoding", { buf = bufnr }) ~= ""
	and vim.api.nvim_get_option_value("fileencoding", { buf = bufnr })
	or vim.api.nvim_get_option_value("encoding", { scope = "global" })
	local encoding = vim.api.nvim_get_option_value("fileencoding", { buf = bufnr })
	if encoding == "" then
	encoding = vim.api.nvim_get_option_value("fileencoding", { scope = "global" })
	end

[zbirenbaum]

LGTM thanks for the fix!