Prevent panic on empty meta with 40/50 response codes

[a-h]

In the case that no meta information is provided when a 40/50 response is returned, amfora currently panics when trying to title case the text and add punctuation. The Gemini "spec" doesn't require meta to be populated, so this case may need to be handled.

The contents of <META> may provide additional information on the failure, and should be displayed to human users.

[makew0rld]

Thanks! Merged.

I should be looking at my string indices more carefully, and what assumptions they have, it seems. Also, could you provide an example of a server that does this, for testing?

[a-h]

My server does this (https://github.com/a-h/gemini) for 51 responses. I couldn't think of anything I wanted to say more than the 51 status already says "not found", maybe I should be more inventive. 😁

I haven't got one a server on the public Internet yet for super-easy testing, but if you use Docker:

# Create a server certificate.
openssl ecparam -genkey -name secp384r1 -out server.key
openssl req -new -x509 -sha256 -key server.key -out server.crt -days 3650
# Make a Gemini file.
mkdir content
echo "# Hello, World!" > content/index.gemini
# Run the container.
docker pull adrianhesketh/gemini:latest
docker run -v `pwd`:/certs -e PORT=1965 -e DOMAIN=localhost -v `pwd`/content:/content -p 1965:1965 adrianhesketh/gemini:latest

You should then be able to get a 51 return value with no meta information by accessing gemini://localhost/not_found

[makew0rld]

Returning just the name of the status code as a META is probably a good practice, it's what the other servers do. But I should definitely still handle this, so thanks :)