base-files: extra sanity checks.

iopsys-brcm63xx-arm/base-files/lib/upgrade/iopsys-4-to-5-migrator.sh

@@ -384,6 +384,8 @@ erase_mtd() {
 #--------------------------------------------------------------
 # Erase a UBI volume $1 (by name) and wait for it to disappear.
 erase_ubi_volume() {
+	[ -n "$1" ] || return 0
+
 	if grep -q "$1" /sys/class/ubi/*/name; then
 		ubirmvol "/dev/ubi0" -N "$1" || return
 
@@ -414,6 +416,7 @@ erase_jffs_kernel() {
 
 	[ $1 -ge 0 -a $1 -le 1 ] || return
 
+	grep -q "kernel_${1}" /sys/class/ubi/*/name && return 0
 	mtd="$(bcm_find_mtd kernel_${1})" || return
 	[ -n "$mtd" ] || return 0
 	[ $mtd -gt 0 ] || return 0