Only use ALAC workaround if sample rate is 0

This prevents the workaround from occuring once FFmpeg has the bug
patched.

extensions/ffmpeg/src/main/java/com/google/android/exoplayer2/ext/ffmpeg/FfmpegDecoder.java

@@ -88,14 +88,13 @@ import java.util.List;
     }
     if (!hasOutputFormat) {
       channelCount = ffmpegGetChannelCount(nativeContext);
-      if ("alac".equals(codecName)) {
+      sampleRate = ffmpegGetSampleRate(nativeContext);
+      if (sampleRate == 0 && "alac".equals(codecName)) {
         // ALAC decoder did not set the sample rate in earlier versions of FFMPEG.
         // See https://trac.ffmpeg.org/ticket/6096
         ParsableByteArray parsableExtraData = new ParsableByteArray(extraData);
         parsableExtraData.setPosition(extraData.length - 4);
         sampleRate = parsableExtraData.readUnsignedIntToInt();
-      } else {
-        sampleRate = ffmpegGetSampleRate(nativeContext);
       }
       hasOutputFormat = true;
     }