Fix for spurious failure in cast_message_util_fuzzer

Bug: 1126456, b/168119924
Change-Id: Ibf372f4eb7c2a75479626a8f542e5b15de461f2a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2405632Reviewed-by: mark a. foltz <mfoltz@chromium.org>
Commit-Queue: John Williams <jrw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#807643}

components/cast_channel/cast_message_util_fuzzer.cc

@@ -159,8 +159,8 @@ DEFINE_PROTO_FUZZER(const CastMessageUtilInputs& input_union) {
       CreateReceiverStatusRequest(input.source_id(), input.request_id());
       break;
     }
-    default:
-      NOTREACHED();
+    case CastMessageUtilInputs::INPUT_NOT_SET:
+      break;
   }
 }