storage: avoid MGET call when no keys are specified (#2156)
storage: avoid MGET call when no keys are specified (#2156)

Fixes #2155 

`GetKeysAndValuesWithFilter` lists keys and runs `MGET`(https://redis.io/commands/mget) using these keys. This patch avoids the `MGET` call when the list is empty.

This method is only called by the `oauth_manager.go` code.
lonelycode/tyk,lonelycode/tyk,lonelycode/tyk