check if backing store exists beforehand

Signed-off-by: Michel-FK <michel.stempin@funkey-project.com>

Recovery/board/funkey/rootfs-overlay/usr/local/sbin/share

@@ -85,7 +85,9 @@ stop_share () {
 start_share () {
 
     # 1) Check if the backing store partition is already shared
-    cat $BACKING_STORE_FILE | egrep -q ^/dev/mmcblk0p3 && die 12 "the backing store partition is already shared"
+    if [ -e $BACKING_STORE_FILE ]; then
+	cat $BACKING_STORE_FILE | egrep -q ^/dev/mmcblk0p3 && die 12 "the backing store partition is already shared"
+    fi
 
     # 2) Check if USB data is connected
     is_usb_data_connected > /dev/null 2>&1 || die 13 "USB sharing impossible, not connected to a host"
@@ -101,6 +103,10 @@ start_share () {
 # Return if currently sharing
 is_share_started () {
 
+    if [ ! -e $BACKING_STORE_FILE ]; then
+	echo "no"
+	return 1
+    fi
     cat $BACKING_STORE_FILE | egrep -q ^/dev/mmcblk0p3
     local res=$?
     if [ "$res" == "0" ]; then