Hyperloglog: refresh hdr variable correctly.
Hyperloglog: refresh hdr variable correctly.

This is a fix for the #3819 improvements. The o->ptr may change because
of hllSparseSet() calls, so 'hdr' must be correctly re-fetched.

JackieXie168/redis,JackieXie168/redis,JackieXie168/redis,JackieXie168/redis