[fuzzing] Be more robust in PrepareFunctionForOptimization

This changes PrepareFunctionForOptimization to have the same checks
as OptimizeFunctionOnNextCall, as otherwise fuzzing runs into
the DCHECK with a bad number of arguments.

Bug: chromium:1094866
Change-Id: Ief7d428a12139c47a74607d39792276a2eae4ebf
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2250255Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68410}

src/runtime/runtime-test.cc

@@ -369,8 +369,9 @@ RUNTIME_FUNCTION(Runtime_EnsureFeedbackVectorForFunction) {
 
 RUNTIME_FUNCTION(Runtime_PrepareFunctionForOptimization) {
   HandleScope scope(isolate);
-  DCHECK(args.length() == 1 || args.length() == 2);
-  if (!args[0].IsJSFunction()) return CrashUnlessFuzzing(isolate);
+  if ((args.length() != 1 && args.length() != 2) || !args[0].IsJSFunction()) {
+    return CrashUnlessFuzzing(isolate);
+  }
   CONVERT_ARG_HANDLE_CHECKED(JSFunction, function, 0);
 
   bool allow_heuristic_optimization = false;