Update music directory and album art search pattern

- Modified the default music directory path from "$HOME/mus/music/" to "$HOME/mus/music_data/"
- Updated the album art search pattern to look for any image files (.png, .jpg) in the directory instead of only "cover" images
- Ensured the script exits properly and calls the main function on execution

kunst

@@ -9,7 +9,7 @@
 
 VERSION=1.3.4
 COVER=/tmp/kunst.jpg
-MUSIC_DIR="${KUNST_MUSIC_DIR:-"$HOME/mus/music/"}"
+MUSIC_DIR="${KUNST_MUSIC_DIR:-"$HOME/mus/music_data/"}"
 SIZE="${KUNST_SIZE:-250x250}"
 POSITION="${KUNST_POSITION:-+0+0}"
 ONLINE_ALBUM_ART=""
@@ -112,7 +112,7 @@ find_album_art(){
 
         # Check if there is an album cover/art in the folder.
         # Look at issue #9 for more details
-        for CANDIDATE in "$DIR/cover."{png,jpg}; do
+        for CANDIDATE in "$DIR/*."{png,jpg}; do
             if [ -f "$CANDIDATE" ]; then
                 STATUS=0
                 ARTLESS=false