Fix XLOOKUP/VLOOKUP/HLOOKUP/MATCH #N/A before dimension

[swmal]

Summary

Fixes a regression introduced in 8.5.0 (still present in 8.6.3) where XLOOKUP, VLOOKUP, HLOOKUP and MATCH return #N/A when the lookup range starts before the first populated cell of the worksheet (lookupRange.Address.FromRow < Worksheet.Dimension.FromRow).

Root cause

In XlookupScanner, GetMaxItemsRow/GetMaxItemsColumns were changed to use GetAddressDimensionAdjusted(0) to avoid iterating over empty rows in open ranges (e.g. A:A). This clamps both ends of the range to the worksheet dimension and returns the clamped size as maxItems.

However, the scanning loop reads values with GetOffset(ix, 0), which is relative to the range's own FromRow/FromCol. When the dimension starts after the range start, maxItems becomes too small and the loop iterates over the empty leading rows, never reaching the actual data.

Fix

The scanner now tracks a startOffset (distance between the range's own start and the clamped start) and iterates GetOffset(startOffset + ix, ...), returning startOffset + ix as the result index.

This keeps the performance optimisation in both directions — leading empty rows and trailing empty rows are still skipped — while offset base and return index stay range-relative and correct. The fix is centralised in the scanner, so it covers all IRangeInfo implementations (RangeInfo, external and in-memory) without touching each GetAddressDimensionAdjusted.