tests: add fuzzer seed file for crash in blob_len

tests: add fuzzer seed file for crash in blob_len

Following regression was introduced in commit 5e75160f4878 ("blobmsg:
fix attrs iteration in the blobmsg_check_array_len()"):

 Thread 1 "test-fuzz" received signal SIGSEGV, Segmentation fault.
  in blob_len (attr=0x6020000100d4) at libubox/blob.h:102
  102             return (be32_to_cpu(attr->id_len) & BLOB_ATTR_LEN_MASK) - sizeof(struct blob_attr);

 blob_len (attr=0x6020000100d4) at /libubox/blob.h:102
 blob_raw_len (attr=0x6020000100d4) at /libubox/blob.h:111
 blob_pad_len (attr=0x6020000100d4) at /libubox/blob.h:120
 blobmsg_check_array_len (attr=0x6020000000d0, type=0, blob_len=10) at /libubox/blobmsg.c:145
 fuzz_blobmsg_parse (data=0x6020000000d0 "\001\004", size=10) at /libubox/tests/fuzz/test-fuzz.c:57

Signed-off-by: Petr Štetiar <ynezz@true.cz>