Correct variables name in flac_to_mp3 script: error if the variable

content had white spaces.

flac_to_mp3

@@ -8,7 +8,7 @@ BITRATE="128k"
 LOG_LEVEL="error"
 
 ## If it's an album
-if [ -d ${ALBUM_NAME} ]; then
+if [ -d "${ALBUM_NAME}" ]; then
   printf 'Convert %s to %s\n' "${ALBUM_NAME}" "${NEW_ALBUM_NAME}"
 
   ## Create the new directory
@@ -28,7 +28,7 @@ if [ -d ${ALBUM_NAME} ]; then
 
 else
   FILE="${ALBUM_NAME}"
-  if [ -f ${FILE} ]; then
+  if [ -f "${FILE}" ]; then
     printf 'Convert %s to %s\n' "${FILE}" "${NEW_FORMAT}"
     avconv -v "${LOG_LEVEL}" -i "${FILE}" -b "${BITRATE}" "${FILE%${OLD_FORMAT}}${NEW_FORMAT}"
   fi