Set a reasonable default for folding options' range limit if unset or incorrect

[rcjsuen]

https://github.com/rcjsuen/dockerfile-language-server-nodejs/blob/e20b891200d825e0e1de2dfad047034639cdfc80/src/server.ts#L141-L145

Instead of returning some undefined value (if unset) or a random string/boolean (if the value is wrong type), we should return Number.MAX_VALUE instead.