Fix incompatibility with Protobuf 22.x.

In version 22.x, the JSON conversion functions return
absl::Status, which is marked nodiscard. Check the ok() function
before printing the output.

Bug: 329747255
Test: presubmit
Change-Id: I46e2f20a26953dc6501f51daecc1a56547a326ab
diff --git a/src/result.cpp b/src/result.cpp
index 0726d34..e0b82a6 100644
--- a/src/result.cpp
+++ b/src/result.cpp
@@ -416,10 +416,11 @@
   google::protobuf::util::JsonPrintOptions options;
 
   options.add_whitespace = true;
-  google::protobuf::util::MessageToJsonString(pb, &json, options);
-
-  std::ostream pb_stream(std::cout.rdbuf());
-  pb_stream << json << std::endl;
+  auto status = google::protobuf::util::MessageToJsonString(pb, &json, options);
+  if (status.ok()) {
+    std::ostream pb_stream(std::cout.rdbuf());
+    pb_stream << json << std::endl;
+  }
 }
 
 std::unique_ptr<Result> Result::FromPb(const dittosuiteproto::Result& pb) {