Fixes memory leak in KItemListViewAccessible

Summary: The KItemListViewAccessible class has a list of QAccessibleInterface pointers in a member variable m_cells. The problem is that when new entries are created, the newly allocated pointer is not stored in the list, only a nullptr is store, this renders the cleanup code in the destructor useless. This patch simply stores the pointer in the list, causing the destructor to correctly free the memory.

Test Plan: I found this issue using address sanitizer. Simply building Dolphin with -fsanitize=address and opening a window caused the memory leak.

Reviewers: #dolphin, jtamate, elvisangelaccio

Reviewed By: #dolphin, jtamate, elvisangelaccio

Subscribers: elvisangelaccio, kfm-devel

Tags: #dolphin

Differential Revision: https://phabricator.kde.org/D14168