Before this fix, configuring the server with:
- performance_schema_events_waits_history_size=0
- performance_schema_events_waits_history_long_size=0
could cause a crash in the performance schema.

These settings to 0 are intended to be valid and supported,
and are in fact working properly in mysql 5.6 and up already.

This fix backports the code fix and test cases from mysql 5.6
to the mysql 5.5 release.