[BUG] Rust panic in teletext subtitle output on negative or malformed PTS timestamps

[NexionisJake]

Summary

TeletextContext::process_page() calls .to_srt_time().expect(...) on both
show_timestamp and hide_timestamp. For teletext streams with uninitialized,
wrap-around, or malformed PTS values, Timestamp can hold a negative value.
to_srt_time() → as_hms_millis() calls i64::try_into::<u64>() which
returns TimestampError::OutOfRangeError for negative values — and .expect()
converts this into an unconditional panic crash.

Location

src/rust/lib_ccxr/src/teletext.rs

• Line ~1010: show_timestamp.to_srt_time().expect("could not format to SRT time")
• Line ~1015: hide_timestamp.to_srt_time().expect("could not format to SRT time")

Code

let start = show_timestamp.to_srt_time().expect("could not format to SRT time");
let end   = hide_timestamp.to_srt_time().expect("could not format to SRT time");

Impact

Any teletext stream with an uninitialized or wrap-around PTS (common in
broadcast captures and partial recordings) crashes CCExtractor unconditionally
at subtitle output time, potentially after processing an entire file successfully.

Suggested Fix

Either propagate the error gracefully:

let start = show_timestamp.to_srt_time().ok()?;  // returns None from process_page()
let end   = hide_timestamp.to_srt_time().ok()?;

Or clamp negative timestamps to zero before formatting:

let safe_show = show_timestamp.max(Timestamp::from_millis(0));
let safe_hide = hide_timestamp.max(Timestamp::from_millis(0));

Environment

• Affects all platforms
• Triggered by teletext streams with negative or malformed PTS values