Fix dataCache being weak and block being nonatomic
Fix dataCache being weak and block being nonatomic

- This is called out by one of the stricter warnings. This patch makes
sure we hold a strong pointer to it throughout the block’s scope.
- Also make sure we don’t create a retain-cycle from the block to the
timer proxy since it’s managed by a queue we potentially own strongly.
By doing the normal self-weakification->strongification dance.

chrisbtreats/SPTPersistentCache,chrisbtreats/SPTPersistentCache,FootballAddicts/SPTPersistentCache,iOSCowboy/SPTPersistentCache,iOSCowboy/SPTPersistentCache,iOSCowboy/SPTPersistentCache,FootballAddicts/SPTPersistentCache,FootballAddicts/SPTPersistentCache,FootballAddicts/SPTPersistentCache,chrisbtreats/SPTPersistentCache,spotify/SPTPersistentCache,spotify/SPTPersistentCache,spotify/SPTPersistentCache,chrisbtreats/SPTPersistentCache