[vm/gardening] Fix unused variable warning due to args evaluation ordering

Bug: https://github.com/dart-lang/sdk/issues/59808
Change-Id: Ief330084f7d3782b126d028a34554a01f22db680
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/402420
Reviewed-by: Samuel Rawlins <srawlins@google.com>
Commit-Queue: Alexander Aprelev <aam@google.com>

samples/embedder/run_kernel.cc

@@ -104,8 +104,8 @@ int main(int argc, char** argv) {
   char* error;
 
   // Start Dart VM.
-  CheckError(dart::embedder::InitOnce(&error), error,
-             "dart::embedder::InitOnce");
+  bool result = dart::embedder::InitOnce(&error);
+  CheckError(result, error, "dart::embedder::InitOnce");
 
   std::vector<const char*> flags{};
   CheckError(Dart_SetVMFlags(flags.size(), flags.data()), "Dart_SetVMFlags");