Rewrite an implementation to reduce compilation time
Rewrite an implementation to reduce compilation time

The coalescing operator for some reasons increases the build times.
On my machine replacing the implementation brings down the compile time `Bag.count` from 1005ms to 13ms

kzaher/RxSwift,cfraz89/RxSwift,KyoheiG3/RxSwift,kzaher/RxSwift,cfraz89/RxSwift,ReactiveX/RxSwift,shiratsu/RxSwift,kzaher/RxSwift,ReactiveX/RxSwift,tottakai/RxSwift,cfraz89/RxSwift,tottakai/RxSwift,cfraz89/RxSwift,tottakai/RxSwift,kzaher/RxSwift,shiratsu/RxSwift,KyoheiG3/RxSwift,shiratsu/RxSwift,KyoheiG3/RxSwift,ReactiveX/RxSwift