Use 'if let' in 'SemaphorePool', because 'if let' is not slow in that context
Use 'if let' in 'SemaphorePool', because 'if let' is not slow in that context

The previous version left a small window open for a race condition leading to dereferencing nil. This version should be impervious to this.

glessard/swift-channels,glessard/swift-channels