Allow NextSegment() to be called across multiple Process() calls in the Go binding

[joshmux]

Summary

Fixes an issue in the Go bindings where calling NextSegment() after multiple Process() invocations returns no new segments. This prevented incremental or streaming-style processing from functioning correctly.

Details

When the Go wrapper calls Process() more than once, the internal context segment counter (context.n) is not reset or updated properly. As a result:

• NextSegment() stops yielding new segments after the first Process() call.
• Incremental processing workflows (e.g., feeding audio in chunks) silently fail.
• The behavior diverges from expectations set by the underlying C++ implementation.

This PR resets context.n at the start of each Process() call, ensuring that segment iteration works correctly across multiple processing passes.

Impact

• Enables proper streaming and incremental recognition in the Go bindings.
• Prevents confusing silent failures where no segments are returned.
• Improves consistency and correctness relative to whisper.cpp core behavior.

Backward Compatibility

This change is internal to the Go bindings and does not modify the public API.
Existing code using a single Process() → NextSegment() workflow will behave exactly as before.