cablev2: treat null arrays as empty.

When a GMSCore FIDO operation fails, it'll return a non-zero status and
null for the other parameters. This change causes the null byte arrays
to be translated into empty spans rather than crashing.

BUG=1002262

Change-Id: Idc3cb81e4ef17216634677e1d595b7357f2fb70e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2463807
Commit-Queue: Adam Langley <agl@chromium.org>
Reviewed-by: Martin Kreichgauer <martinkr@google.com>
Cr-Commit-Position: refs/heads/master@{#816602}

chrome/android/features/cablev2_authenticator/native/cablev2_authenticator_android.cc

@@ -77,6 +77,10 @@ NewState() {
 base::span<const uint8_t> JavaByteArrayToSpan(
     JNIEnv* env,
     const JavaParamRef<jbyteArray>& data) {
+  if (data.is_null()) {
+    return base::span<const uint8_t>();
+  }
+
   const size_t data_len = env->GetArrayLength(data);
   const jbyte* data_bytes = env->GetByteArrayElements(data, /*iscopy=*/nullptr);
   return base::as_bytes(base::make_span(data_bytes, data_len));