lock.sh: Use xset in a sane way to re-blank screen on idle during lock

.config/i3/lock.sh

@@ -16,14 +16,11 @@ lock() {
 
 case "$1" in
     lock)
-        lock
-
-        # if given an argument, turn off the screen after that many seconds
-        if [[ $2 && ${2-x} ]]
-        then
-            sleep $2
-            xset dpms force off
-        fi
+        trap "xset dpms 0 0 0" HUP INT TERM
+        # set dpms time to argument, or 0 if none given
+        xset +dpms dpms ${2-0} ${2-0} ${2-0}
+        lock ${2+"--nofork"}
+        xset dpms 0 0 0
         ;;
     logout)
         i3-msg exit