Fixes small memory leak in DolphinContextMenu
Summary: When DolphinContextMenu::baseFileItem is called a KFileItem is allocated and stored in DolphinContextMenu::m_baseFileItem, which is of type KFileItem*, but the destructor failed to delete this.
Test Plan: This leak was found using Address Sanitizer
Reviewers: broulik, elvisangelaccio
Reviewed By: broulik, elvisangelaccio
Subscribers: ngraham, kfm-devel
Differential Revision: https://phabricator.kde.org/D14178