SAN FRANCISCO — The creators of the famous Forbes rich list have made their first attempt to identify the wealthiest people in the virtual currency industry. Yet the list that was published on Wednesday, right after major drops in virtual currency prices, inadvertently also served as a reminder of the fleeting nature of that wealth. While the list in Forbes magazine, which was assembled in recent weeks, identifies about 10 virtual currency billionaires, most of them were not billionaires by the time the feature went online on Wednesday morning.