Fix active expire division by zero.
Fix active expire division by zero.

Likely fix #6723.

This is what happens AFAIK: we enter the main loop where we expire stuff
until a given percentage of keys is still found to be logically expired.
There are however other potential exit conditions.

However the "sampled" variable is not always incremented inside the
loop, because we may found no valid slot as we scan the hash table, but
just NULLs ad dict entries. So when the do/while loop condition is
triggered at the end, we do (expired*100/sampled), dividing by zero if
we sampled 0 keys.

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