fix the empty cell value edit crash

[startewho]

when i set a TextColumn like this:

   new TextColumn<Country, int>("GDP", x => x.GDP,(x,n)=>{ }, new GridLength(3, GridUnitType.Star), new()

and i edit the GDP value by empty string,like backspace the value.and then enter

the app crash,the reason is that

System.FormatException: The input string '' was not in a correct format.
11:20:17:288	   at System.Number.ThrowFormatException[TChar](ReadOnlySpan`1 value)
11:20:17:288	   at System.String.System.IConvertible.ToInt32(IFormatProvider provider)
11:20:17:288	   at System.Convert.ChangeType(Object value, Type conversionType, IFormatProvider provider)
11:20:17:288	   at Avalonia.Controls.Models.TreeDataGrid.TextCell`1.set_Text(String value) in /_/src/Avalonia.Controls.TreeDataGrid/Models/TreeDataGrid/TextCell.cs:line 52

[startewho]

will the fix be merged soon, we have a product depend it.

[MikeCodesDotNET]

will the fix be merged soon, we have a product depend it.

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