AWR Browser: Wrong numbers after startup

New wait_time_milli is only tracked by dba_hist_event_histogram once it has been encountered for the first time.


Calculation currently used by TOAD:
e.wait_count - lag(e.wait_count, 1) over (order by e.event_id, e.wait_time_milli, e.snap_id) waits

This leads to wrong (and usually negative) numbers when a wait_time_milli occurs for the first time:

The calculation should something like:
e.wait_count - NVL( lag(e.wait_count, 1) over (partition by e.dbid, e.instance_number, e.event_id, e.wait_time_milli order by e.snap_id), 0 ) waits

that makes sense. Done for next beta.