Bugfixing config script alternc_html trailing slash since with the get_first_existing_dir function

we might end up with an empty variable.

debian/alternc.config

@@ -211,7 +211,7 @@ while [ "$QUEST_STATE" != 0 -a "$QUEST_STATE" != 13 ]; do
     ALTERNC_HTML="$RET"
     #checking acl and quota activation.
     basedir=`get_first_existing_dir "$ALTERNC_HTML"`;
-    MOUNT_POINT=$(df -P ${basedir%/*} | tail -n 1 | awk '{print $6}')
+    MOUNT_POINT=$(df -P ${basedir} | tail -n 1 | awk '{print $6}')
     #we get the first existing dir
     aclcheckfile="$basedir/test-acl"
     touch "$aclcheckfile"