Cannot run custom-query without any integer ranges.

[Pommaq]

Found this while working on tests for #23 .

thread 'main' panicked at crates/producer/src/custom_query.rs:54:70:
called `Result::unwrap()` on an `Err` value: ParseIntError { kind: Empty }
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

The prompt I used was
cargo run -- -f examples/ALICE_BANK_STATEMENT.pdf custom-query "I'M BATMAN"

Removing the single-tick (') still caused the same error.

Runnning
cargo run -- -f examples/ALICE_BANK_STATEMENT.pdf custom-query "I'M BATMAN{1337}"
produces

thread 'main' panicked at crates/producer/src/custom_query.rs:56:33:
called `Option::unwrap()` on a `None` value
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

I suggest either resolving this or ensure we report a cleaner error message.