This is a repeat of commit de6ced6692
"QCborValue: fix incorrect to{Array,Map} when the value is empty" (6.4),
which fixed the same thing for QCborValue. I've just copied the exact
same implementation onto the QJsonValue functions.
Pick-to: 6.2 6.3 6.4 5.15
Fixes: QTBUG-104085
Change-Id: I175efddd75f24ae59057fffd16f6b257bf7ed36d
Reviewed-by: Sona Kurazyan <sona.kurazyan@qt.io>