Resolve possible memory leaks in Keychain functions

[Eitot]

CoreFoundation API do not use ARC. The SecItemCopyMatching(,) function returns an owning reference to the CFTypeRef it passes back. By using __bridge_transfer instead of __bridge, the pointer is bridged to an Objective-C object and then its memory is managed by ARC.

Local variable pointers to CoreFoundation objects do not appear to be set to NULL by default, unlike Objective-C pointers when ARC is enabled. As a precaution, the initial value of those variables is set to NULL.

See:

• https://developer.apple.com/library/archive/releasenotes/ObjectiveC/RN-TransitioningToARC/Introduction/Introduction.html
• https://developer.apple.com/library/archive/documentation/CoreFoundation/Conceptual/CFDesignConcepts/Articles/tollFreeBridgedTypes.html