Make mp4 chapters optional.

encode.bash

@@ -146,6 +146,8 @@ faac -q ${aac_quality} \
 --cover-art "${cover}" \
 ${base_file}.wav
 
+if [ -f ${aac_notes_path}/${date}.notes ]
+then
 	# put together the just-so input file for mp4chaps
 	echo "00:00:00.000 Start" > \
 	${base_file}.chapters.txt
@@ -155,6 +157,7 @@ ${base_file}.chapters.txt
 
 	# write the chapter marks to the AAC/MP4 file
 	mp4chaps -o -z -i ${base_file}.m4a
+fi
 
 echo ""
 echo "Encoding ${base_file}.ogg at quality ${ogg_quality}."