Fix typo in comment (#715)

Author: sbooth

Sources/CSFBAudioEngine/Player/AudioPlayer.h

@@ -246,7 +246,7 @@ class AudioPlayer final {
 private:
 	/// Possible bits in `flags_`
 	enum class Flags : unsigned int {
-		/// Cached value of `_audioEngine.isRunning`
+		/// Cached value of `engine_.isRunning`
 		engineIsRunning				= 1u << 0,
 		/// The render block is outputting audio
 		isPlaying 					= 1u << 1,