bootutil/bootutil_public: Treat unreachable image swap state as empty

Treat state of unreachable image device as if it is empty image.

This is required for boot the primary image if it is still available.

Signed-off-by: Andrzej Puzdrowski <andrzej.puzdrowski@nordicsemi.no>

Author: nvlsianpu

boot/bootutil/src/bootutil_public.c

@@ -425,7 +425,15 @@ boot_swap_type_multi(int image_index)
 
     rc = boot_read_swap_state_by_id(FLASH_AREA_IMAGE_SECONDARY(image_index),
                                     &secondary_slot);
-    if (rc) {
+    if (rc == BOOT_EFLASH) {
+        BOOT_LOG_INF("Secondary image of image pair (%d.) "
+                     "is unreachable. Treat it as empty", image_index);
+        secondary_slot.magic = BOOT_MAGIC_UNSET;
+        secondary_slot.swap_type = BOOT_SWAP_TYPE_NONE;
+        secondary_slot.copy_done = BOOT_FLAG_UNSET;
+        secondary_slot.image_ok = BOOT_FLAG_UNSET;
+        secondary_slot.image_num = 0;
+    } else if (rc) {
         return BOOT_SWAP_TYPE_PANIC;
     }