src: add check for Bignum in GroupOrderSize

I think it's missed, cause in this file we have example of checking
result of BignumPointer::new

Refs: #56692

Author: wooffie

src/crypto/crypto_ec.cc

@@ -937,6 +937,7 @@ size_t GroupOrderSize(const EVPKeyPointer& key) {
   const EC_KEY* ec = key;
   CHECK_NOT_NULL(ec);
   auto order = BignumPointer::New();
+  CHECK(order);
   CHECK(EC_GROUP_get_order(ECKeyPointer::GetGroup(ec), order.get(), nullptr));
   return order.byteLength();
 }