Wt

There seem to be various issues with WAbstractItemModel implementations (e.g. WStandardItemModel), when appending, inserting, or removing items, rows, or columns.
The model doesn't seem to:

• always resize correctly, resulting in an unexpected model layout.
• insert empty items correctly, resulting in nullptr entries.

These have been noticed so far, more may be applicable. The functionality ought to be corrected, to produce the expected outcome, and tests should be added to ensure that the functionality is correct.