taproot: fix merkle path length check

Per BIP-0341 path lengths are limited to 128 or less.

Author: jgriffiths

src/map.c

@@ -667,7 +667,9 @@ int wally_merkle_path_xonly_public_key_verify(const unsigned char *key, size_t k
 
     if (key_len != EC_XONLY_PUBLIC_KEY_LEN ||
         keypath_key_verify(key, key_len, &extkey) != WALLY_OK ||
-        extkey.version || BYTES_INVALID(val, val_len) || val_len % SHA256_LEN != 0)
+        extkey.version || BYTES_INVALID(val, val_len))
+        return WALLY_EINVAL;
+    if (val_len && (val_len % SHA256_LEN || val_len % SHA256_LEN > 128u))
         return WALLY_EINVAL;
     return WALLY_OK;
 }