Fix building desktop CDs with easy-build.sh

Closes: #740558, patch from Samuel Thibault

debian/changelog

@@ -6,6 +6,7 @@ debian-cd (3.1.15) UNRELEASED; urgency=low
 
   [ Samuel Thibault ]
   * Make kfreebsd & hurd images usbkey-bootable. Closes: #739422
+  * Fix building desktop CDs with easy-build.sh Closes: #740558
 
   [ Raphaël Hertzog ]
   * Fix code extracting the xorriso version.

easy-build.sh

@@ -150,7 +150,7 @@ esac
 
 # By default a GNOME CD/DVD is built, but other desktops are supported too
 if [ "$desktop" ]; then
-	if [ ! -e tasks/$CODENAME/task.list.$desktop ]; then
+	if [ ! -e tasks/$CODENAME/Debian-$desktop ]; then
 		echo "Error: desktop '$desktop' is not supported for $CODENAME"
 		exit 1
 	fi