go back to page 1 when data is updated and you are on a page that no longer exists

[chriddyp]

see https://community.plot.ly/t/unavoidable-circular-dependency-when-using-backend-paging-and-filtering-with-datatables-feature-request/35161/2

if page_current > page_count , force page_current = page_count by changing page_current

or perhaps we go back to page 1?