Fix null reference in DataGrid layout rounding scroll logic#243
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The changes make sense. The returned values from GetPrevious/NextVisibleScrollingColumn could definitely be null.
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Updated [Avalonia](https://github.com/AvaloniaUI/Avalonia/) from 12.0.4 to 12.0.5. <details> <summary>Release notes</summary> _Sourced from [Avalonia's releases](https://github.com/AvaloniaUI/Avalonia//releases)._ No release notes found for this version range. Commits viewable in [compare view](https://github.com/AvaloniaUI/Avalonia//commits). </details> Updated [Avalonia.Controls.DataGrid](https://github.com/AvaloniaUI/Avalonia.Controls.DataGrid) from 12.0.0 to 12.0.1. <details> <summary>Release notes</summary> _Sourced from [Avalonia.Controls.DataGrid's releases](https://github.com/AvaloniaUI/Avalonia.Controls.DataGrid/releases)._ ## 12.0.1 ## What's Changed * Update DataGridColumn sort binding checks by @rabbitism in AvaloniaUI/Avalonia.Controls.DataGrid#230 * Fix template column edit commit and context menu regression in DataGrid_LostFocus by @kdurane in AvaloniaUI/Avalonia.Controls.DataGrid#235 * Fix null reference in DataGrid layout rounding scroll logic by @zrt2399 in AvaloniaUI/Avalonia.Controls.DataGrid#243 * Fix ScrollBar not reacting to ScrollViewer.AllowAutoHide property changes by @zrt2399 in AvaloniaUI/Avalonia.Controls.DataGrid#241 * Update Avalonia to 12.0.5 by @MrJul in AvaloniaUI/Avalonia.Controls.DataGrid#246 **Full Changelog**: AvaloniaUI/Avalonia.Controls.DataGrid@12.0.0...12.0.1 Commits viewable in [compare view](https://github.com/AvaloniaUI/Avalonia.Controls.DataGrid/commits/12.0.1). </details> Updated [Avalonia.Desktop](https://github.com/AvaloniaUI/Avalonia/) from 12.0.4 to 12.0.5. <details> <summary>Release notes</summary> _Sourced from [Avalonia.Desktop's releases](https://github.com/AvaloniaUI/Avalonia//releases)._ No release notes found for this version range. Commits viewable in [compare view](https://github.com/AvaloniaUI/Avalonia//commits). </details> Updated [Avalonia.Fonts.Inter](https://github.com/AvaloniaUI/Avalonia/) from 12.0.4 to 12.0.5. <details> <summary>Release notes</summary> _Sourced from [Avalonia.Fonts.Inter's releases](https://github.com/AvaloniaUI/Avalonia//releases)._ No release notes found for this version range. Commits viewable in [compare view](https://github.com/AvaloniaUI/Avalonia//commits). </details> Updated [Avalonia.Themes.Fluent](https://github.com/AvaloniaUI/Avalonia/) from 12.0.4 to 12.0.5. <details> <summary>Release notes</summary> _Sourced from [Avalonia.Themes.Fluent's releases](https://github.com/AvaloniaUI/Avalonia//releases)._ No release notes found for this version range. Commits viewable in [compare view](https://github.com/AvaloniaUI/Avalonia//commits). </details> Signed-off-by: dependabot[bot] <support@github.com> Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
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Fix a layout-rounding edge case in DataGrid.ComputeDisplayedColumns.
When UseLayoutRounding is enabled, column layout can differ slightly from the logical ActualWidth-based scrolling calculations due to pixel rounding. After resizing and maximizing the window, this can leave a small positive horizontal offset even though the first displayed scrolling column is already the first visible scrolling column.
In that state, GetPreviousVisibleScrollingColumn(...) correctly returns null, because there is no previous scrolling column. The existing code assumed a previous column must exist whenever _horizontalOffset > 0, which could lead to a null dereference.
This change handles that boundary condition explicitly. If no previous visible scrolling column exists, the grid clamps the horizontal offset state back to zero and marks the displayed column state as invalidated. Otherwise, it preserves the existing behavior for partially scrolling in the previous column.
This prevents a crash while keeping the scroll/display state consistent with the actual leftmost scrolling column.