Add test to make sure geodist with a missing member returns None
Add test to make sure geodist with a missing member returns None

Fixes #939

alisaifee/redis-py,redis/redis-py,mozillazg/redis-py-doc,andymccurdy/redis-py,andymccurdy/redis-py,andymccurdy/redis-py,5977862/redis-py,5977862/redis-py,redis/redis-py,alisaifee/redis-py,5977862/redis-py,mozillazg/redis-py-doc