Ledger view remains disabled after switching to a different file.
This was caused by the fact that the accounts model was not loaded by the time the account selector in the ledger was being used to set the visible account.

This means that at that time the visible account could not be set.

After the accounts model gets loaded nobody tried to set the ledger's visible account which is correct.
Fix this problem by making sure that the accounts model is loaded by the time the ledger's visible account is being set.

Do this by activating the "load on idle" feature only if there is a real account loaded not after the first time like it was done before.

+ A small step in improving the performance issue. Load the accounts model on idle instead of when dataChanged() is emitted when it's possible.

Backport to the stable branch.