av_dump_format: add a heading for chapters

Otherwise the chapters look like a part of the metadata section.

libavformat/dump.c

@@ -686,6 +686,8 @@ void av_dump_format(AVFormatContext *ic, int index,
         av_log(NULL, AV_LOG_INFO, "\n");
     }
 
+    if (ic->nb_chapters)
+        av_log(NULL, AV_LOG_INFO, "  Chapters:\n");
     for (i = 0; i < ic->nb_chapters; i++) {
         const AVChapter *ch = ic->chapters[i];
         av_log(NULL, AV_LOG_INFO, "    Chapter #%d:%d: ", index, i);