Fix problems for older ffmpeg versions

Fix the following issues when building against older ffmpeg versions

- the call to avcodec_free_context exceptions as avformat_close_input
  already performs cleanup of the AVCodecContext, so link the calling of
  avcodec_free_context in k3bffmpegwrapper.cpp to the version of
  libavformat in which codecpar appeared rather than when
  avcodec_free_context appeared.
- avcodec_decode_audio4 was deprecated in libavcodec 57.106.100, not
  57.12.100, so the version has been corrected.

Signed-off-by: aneejit1 <aneejit1@gmail.com>

plugins/decoder/ffmpeg/k3bffmpegwrapper.cpp

@@ -232,7 +232,7 @@ void K3bFFMpegFile::close() {
   d->packetData = NULL;
 
   if (d->codec) {
-#if LIBAVCODEC_VERSION_INT >= AV_VERSION_INT(55, 63, 100)
+#if LIBAVFORMAT_VERSION_INT >= AV_VERSION_INT(57, 33, 100)
     ::avcodec_free_context(&d->audio_stream_ctx);
 #else
     ::avcodec_close(d->audio_stream_ctx);
@@ -358,7 +358,7 @@ int K3bFFMpegFile::fillOutputBuffer() {
     }
 
     int gotFrame = 0;
-#if LIBAVCODEC_VERSION_INT >= AV_VERSION_INT(57, 12, 100)
+#if LIBAVCODEC_VERSION_INT >= AV_VERSION_INT(57, 106, 100)
     int len = avcodec_receive_frame(d->audio_stream_ctx, d->frame);
     if (len == 0) {
       gotFrame = 1;