Mark Johnston 6ac0e4858a Let the standard deviation of the empty set be 0. This is consistent with
the behaviour for averages, and fixes a crash that can occur when attempting
to print a stddev aggregation containing no elements:

    dtrace:::BEGIN { @ = stddev(0); clear(@); printa("%@d", @); }

PR:		197260
MFC after:	2 week
2015-02-02 20:48:31 +00:00
..
2015-01-31 23:12:29 +00:00
2014-08-22 22:13:36 +00:00