API: Fix FileRange validation order to reject negative offset/length

[manuzhang]

Apache Iceberg version

main (development)

Query engine

None

Please describe the bug 🐞

FileRange currently validates length() and offset() before assigning constructor parameters to fields. Because those getters return default field values at that point, negative constructor inputs can bypass validation.

This allows malformed ranges to propagate into vectored reads and trigger runtime failures.

Willingness to contribute

• I can contribute a fix for this bug independently
• I would be willing to contribute a fix for this bug with guidance from the Iceberg community
• I cannot contribute a fix for this bug at this time

[aviralgarg05]

Hi I would like to solve this issue if someone could assign me

[barry3406]

Just a heads up that PR #15926 (already approved) addresses this — happy to coordinate with @aviralgarg05 if there's overlap.