fix: lsp crashes on wrong definitions

[mduthey]

Following the next example

tx crash_transaction() {
  output {
    to: "addr_...",
    datum: WrongRecord {
      ship_counter: 1,
    },
  }
}

as WrongRecord isn't defined lsp server will crash

[Info  - 12:26:16 p.m.] server initialized!

thread 'main' panicked at /Users/mduthey/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/tx3-lang-0.4.1/src/analyzing.rs:454:18:
internal error: entered unreachable code
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
[Error - 12:26:16 p.m.] The Tx3 Language Server server crashed 5 times in the last 3 minutes. The server will not be restarted. See the output for more information.