[wasm][fuzzer] Fix instantiation in fuzzer

Reset the instance before the test run, to ensure it runs with the
same initial state as the reference run.

R=clemensb@chromium.org

Bug: chromium:1227591
Change-Id: Ie78b4b84e3df37ab8955c240f1d41e2f5e89a5de
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3015572
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75658}

test/fuzzer/wasm-fuzzer-common.cc

@@ -142,6 +142,15 @@ void InterpretAndExecuteModule(i::Isolate* isolate,
       DCHECK(interpreter_result.trapped());
       exception_ref = true;
     }
+    // Reset the instance before the test run.
+    {
+      ErrorThrower thrower(isolate, "Second Instantiation");
+      // We instantiated before, so the second instantiation must also succeed:
+      CHECK(GetWasmEngine()
+                ->SyncInstantiate(isolate, &thrower, module_object, {},
+                                  {})  // no imports & memory
+                .ToHandle(&instance));
+    }
   } else {
     Handle<WasmInstanceObject> instance_ref;
     {