ios player provide duration on prepare (react-native-audio-toolkit#225)

Author: tbenr

ios/ReactNativeAudioToolkit/ReactNativeAudioToolkit/AudioPlayer.m

@@ -232,7 +232,7 @@ - (NSURL *)findUrlForPath:(NSString *)path {
     // Callback when ready / failed
     if (player.currentItem.status == AVPlayerStatusReadyToPlay) {
         player.automaticallyWaitsToMinimizeStalling = false;
-        callback(@[[NSNull null]]);
+        callback(@[[NSNull null],@{@"duration": @(CMTimeGetSeconds(player.currentItem.asset.duration) * 1000)}]);
     } else {
         NSDictionary* dict = [Helpers errObjWithCode:@"preparefail"
                                          withMessage:[NSString stringWithFormat:@"Preparing player failed"]];