Since https://git.reviewboard.kde.org/r/111989/, the "Create New..." menu in the context menu that appears when right-clicking a folder is not a child of the DolphinMainWindow any more, but of the context menu itself. This seems to be the reason why the dialog that asks for a file name when choosing one of the "Create New..." options disappears immediately.

This patch makes sure that the main window is the parent of the "Create New..." menu again.

Fixes the problem for me.