p910nd: init: check device (/dev/usb/lpX) existence

this prevents the daemon exiting when a configured device
is not plugged in.

Signed-off-by: Paul Donald <newtwen@gmail.com>
(cherry picked from commit dabeaa7643)

net/p910nd/files/p910nd.init

@@ -32,7 +32,9 @@ start_service() {
 start_p910nd() {
 	local section="$1" runas_root
 	config_get_bool "enabled" "$section" "enabled" '0'
-	if [ "$enabled" -gt 0 ]; then
+	config_get device "$section" device
+	# If the device path exists, the device is connected; set it up:
+	if [ "$enabled" -gt 0 ] && [ -e "$device" ]; then
 		args="-d "
 		config_get port "$section" port
 		append_bool "$section" bidirectional "-b"