CMake fix for empty prefix string
CMake fix for empty prefix string

tzapzoor/marble,tucnak/marble,tzapzoor/marble,tzapzoor/marble,tucnak/marble,tucnak/marble,tzapzoor/marble,tzapzoor/marble,tucnak/marble,tucnak/marble,tucnak/marble,tucnak/marble,tzapzoor/marble,tzapzoor/marble,tzapzoor/marble