fix volumesh for mpd

user/scripts/volumesh

@@ -1,5 +1,7 @@
 #!/bin/sh
 
+set -xe
+
 # depends on: awk, pactl, pacmd, notify-send
 
 MAX_VOL=150
@@ -72,7 +74,13 @@ is_muted_mpd() {
     env LC_ALL=C mpc status | grep '\[paused\]' 1>/dev/null
 }
 change_vol_mpd() {
-    mpc vol "${1}${2}" &>/dev/null
+    case $1 in
+        d)
+            op="-";;
+        i)
+            op="+";;
+    esac
+    mpc vol "${op}${2}" &>/dev/null
     round_vol
     mpc vol "${newvol}" &>/dev/null
 }