[wasm][fuzzer] Fix instantiation in fuzzer

Instantiation was inside a DCHECK and therefore did not happen in
non-debug modes. Turn the DCHECK into a CHECK.

R=clemensb@chromium.org

Bug: chromium:1227685
Change-Id: I13240109326a2c94576f6651963543187d96ad3e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3017806Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75673}

test/fuzzer/wasm-fuzzer-common.cc

@@ -155,10 +155,11 @@ void InterpretAndExecuteModule(i::Isolate* isolate,
     Handle<WasmInstanceObject> instance_ref;
     {
       ErrorThrower thrower(isolate, "WebAssembly Instantiation");
-      DCHECK(GetWasmEngine()
-                 ->SyncInstantiate(isolate, &thrower, module_ref, {},
-                                   {})  // no imports & memory
-                 .ToHandle(&instance_ref));
+      // We instantiated before, so the second instantiation must also succeed:
+      CHECK(GetWasmEngine()
+                ->SyncInstantiate(isolate, &thrower, module_ref, {},
+                                  {})  // no imports & memory
+                .ToHandle(&instance_ref));
     }
     result_ref = testing::CallWasmFunctionForTesting(
         isolate, instance_ref, "main", static_cast<int>(compiled_args.size()),