[GNC] Import QIF into placeholder

[Fred Tydeman]

Doing a File: Import: Import QIF
of stock brokerage transactions,
some of them end up in a placeholder account.
This mainly happens for cash transactions.
They end up in the parent account, which is the brokerage account;
which is a placeholder account.
It would be better if the import process warned about this error.

After the import is done, I manually correct those transactions.

I am running Gnucash 5.8 on Fedora Linux 40