`jq_reset` calls `jv_free` on the `exit_code` and the `error_message` stored on the jq state.
However, it doesn't replace the actual instance of those members. This means that subsequent
calls to `jq_reset` will call `jv_free` again on those members, which in turn may call `free`
on the same pointer multiple times. Freeing the same pointer multiple times is undefined
behavior and can cause heap corruption, which is how I spotted this issue.
In practice, this issue only occurs when using a program that may `halt_error`, because that
is when the `exit_code` and `error_message` are set to values other than `jv_invalid`.
Subsequent attempts to call `jq_start` (which calls `jq_reset` internally) after hitting a
`halt_error` can cause you to run into this issue.
The changes simply reset the `exit_code` and the `error_message` to `jv_invalid` (the initial
value set in `jq_init`) after they are freed.
