git_prompt_info: ignore git-config errors
git_prompt_info: ignore git-config errors

Merged from #2906

The function `git_prompt_info` calls `git config` for its stdout output,
but doesn't handle the stderr output.  This can lead to problems,
e.g. if the git config file is unreadable for some reason (permissions
etc).

This fixes the issue by simply ignoring the stderr output.

erwinvaneijk/oh-my-zsh,erwinvaneijk/oh-my-zsh