Summary:
Pull Request resolved: https://github.com/facebook/rocksdb/pull/14581
In `MultiScanIndexIterator::Seek()` Case 3, when re-entering a scan range
after all ranges were exhausted, `block_idx = std::max(cur_scan_start_idx,
cur_idx_)` could produce an out-of-bounds value because `cur_idx_` was left
at `block_handles_.size()` from previous exhaustion. `SeekToBlockIdx()`
unconditionally set `valid_ = true` without checking bounds, causing the
subsequent `value()` call to hit the assertion
`cur_idx_ < block_handles_.size()`.
Added bounds check before `SeekToBlockIdx()` in Case 3 to correctly report
exhaustion instead of crashing.
Reviewed By: joshkang97
Differential Revision: D99604049
fbshipit-source-id: 9d5d91afde7c0984a7b4c2f62604f27f19b07922
ede2cbd67b