error when COHOST_COOKIE is set but empty is unhelpful

[delan]

this happens when doing read -r COHOST_COOKIE; export COHOST_COOKIE in fish.

$ COHOST_COOKIE= cargo run -r -- cohost2json delan chosts
    Finished `release` profile [optimized + debuginfo] target(s) in 0.12s
     Running `/cuffs/code/autost/target/release/autost cohost2json delan chosts`
2024-12-18T02:10:14.335217Z  INFO autost::command::cohost2json: COHOST_COOKIE is set; output will include private or logged-in-only chosts!
Error:
   0: error decoding response body
   1: missing field `result` at line 1 column 151

Location:
   /cuffs/code/autost/src/command/cohost2json.rs:32

Backtrace omitted.
Run with RUST_BACKTRACE=1 environment variable to display it.
Run with RUST_BACKTRACE=full to include source snippets.