fix(fcoe-uefi): exit early on empty vlan

Exit early in case get_fcoe_boot_vlan exits with error or just an empty string,
instead of producing invalid config entry.

Author: pvalena

modules.d/95fcoe-uefi/parse-uefifcoe.sh

@@ -10,8 +10,12 @@ print_fcoe_uefi_conf() {
     [ -z "$mac" ] && return 1
     dev=$(set_ifname fcoe "$mac")
     vlan=$(get_fcoe_boot_vlan "$1")
-    if [ "$vlan" -ne "0" ]; then
+
+    if [ "$vlan" != "0" ]; then
         case "$vlan" in
+            '')
+                return 1
+                ;;
             [0-9]*)
                 printf "%s\n" "vlan=$dev.$vlan:$dev"
                 dev="$dev.$vlan"