Fixes two bugs that appeared since the introduction of the struct:
- when reading permissions from the journal, null ("") was read as
empty-not-null
- when reading permissinos from the server, empty ("") was read as null
Addresses #4608
Create a specific type that parses the permissions so we can store
it in a short rather than in a QByteArray
Note: in RemotePermissions::toString, we make sure the string is not
empty by adding a space, this was already existing before commit
e8f7adc7ca where it was removed by mistake.
Kevin Ottens