Fix for critical error (DataTables warning) 

This commit fixes the error "DataTables warning (table id = 'chain'): DataTables warning: JSON data from server could not be parsed. This is caused by a JSON formatting error."

Thanks to ky_storm.
https://bitcointalk.org/index.php?topic=22785.msg6783064#msg6783064

Polcoin chain doesn't matter here.