fix: frozen-bottom hit testing resolves the wrong row when data is shorter than the viewport

[ghiscoding]

Port bug fix from 6pac/SlickGrid PR 6pac/SlickGrid#1258 into slickgrid-universal

The bug

In frozenBottom mode, getCellFromEvent() and setActiveCellInternal() computed the bottom-canvas row offset from a live measurement of the top canvas:

rowOffset = (this._options.frozenBottom) ? Utils.height(this._canvasTopL) as number : this.frozenRowsHeight;

But the render path places bottom-canvas rows using getFrozenRowOffset(). The two diverge whenever the dataset is shorter than the viewport, because updateRowCount floors the body canvas height at the viewport height:

this.th = Math.max(scrollableRowsHeight, tempViewportH - scrollbarH);
…
Utils.height(this._canvasTopL, this.h);   // ≈ viewport height, not content height

So with e.g. 8 rows × 25px in a 500px container, the live measurement reads ~443px while the rows were placed with a 175px offset — clicking the frozen bottom row resolves to a row ~10 rows away (wrong getCellFromEvent result, wrong active cell).

The fix

Both call sites now use getFrozenRowOffset(this.actualFrozenRow) — the exact offset the render path used to place the row (hit-testing must invert rendering, not re-measure). For the top-freeze branch this is behavior-identical: getFrozenRowOffset returns frozenRowsHeight there.

Repro

{ frozenRow: 1, frozenBottom: true }, 8 rows, 500px-tall container → click the frozen bottom row → pre-fix getCellFromEvent returns a wrong row (e.g. 17 instead of 7).

Test

cypress/e2e/quirk-frozen-bottom-hit-testing.cy.ts — the repro page synthesizes clicks at real cell rects (frozen-bottom row, a body row, and a top-freeze control grid to guard the unchanged branch) and asserts getCellFromEvent resolves the correct rows. Verified to fail pre-fix and pass post-fix; frozen + editing suites ran 28/28 as a regression gate (the fix touches the active-cell path).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.0%. Comparing base (15d9833) to head (d4051b1).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2673   +/-   ##
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  Coverage   100.0%   100.0%           
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  Files         200      200           
  Lines       25452    25452           
  Branches     8999     8997    -2     
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  Hits        25452    25452           

Flag	Coverage Δ
angular	100.0% <ø> (ø)
universal	100.0% <100.0%> (ø)

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commit: d4051b1