[PATCH] Fix invalid pointer return with QGridLayout::itemAt(-1)

[PATCH] Fix invalid pointer return with QGridLayout::itemAt(-1)

QGridLayout::takeAt() and QLayoutItem *itemAt() only check the upper bound.
If the index < 0, these function will return invalid pointer.

Fixes: QTBUG-91261
Pick-to: 5.15 6.0 6.1
Change-Id: Idfb9fb6228b9707f817353b04974da16205a835c
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
Gbp-Pq: Name fix-invalid-pointer-return-with-QGridLayout.diff