Use old guard-let syntax to gain Swift 5.6 compatability

Author: exPHAT

Sources/SwiftWhisper/Whisper.swift

@@ -45,7 +45,8 @@ public class Whisper {
  // swiftlint:disable line_length
  params.new_segment_callback = { (ctx: OpaquePointer?, _: OpaquePointer?, newSegmentCount: Int32, userData: UnsafeMutableRawPointer?) in
  // swiftlint:enable line_length
- guard let ctx, let userData else { return }
+ guard let ctx = ctx,
+ let userData = userData else { return }
  let whisper = Unmanaged<Whisper>.fromOpaque(userData).takeUnretainedValue()
  guard let delegate = whisper.delegate else { return }
 
@@ -73,7 +74,7 @@ public class Whisper {
  }
 
  params.encoder_begin_callback = { (_: OpaquePointer?, _: OpaquePointer?, userData: UnsafeMutableRawPointer?) in
- guard let userData else { return true }
+ guard let userData = userData else { return true }
  let whisper = Unmanaged<Whisper>.fromOpaque(userData).takeUnretainedValue()
 
  if whisper.cancelCallback != nil {
@@ -86,7 +87,7 @@ public class Whisper {
  // swiftlint:disable line_length
  params.progress_callback = { (_: OpaquePointer?, _: OpaquePointer?, progress: Int32, userData: UnsafeMutableRawPointer?) in
  // swiftlint:enable line_length
- guard let userData else { return }
+ guard let userData = userData else { return }
  let whisper = Unmanaged<Whisper>.fromOpaque(userData).takeUnretainedValue()
 
  DispatchQueue.main.async {
@@ -96,7 +97,7 @@ public class Whisper {
  }
 
  private func cleanupCallbacks() {
- guard let unmanagedSelf else { return }
+ guard let unmanagedSelf = unmanagedSelf else { return }
 
  unmanagedSelf.release()
  self.unmanagedSelf = nil