[wasm] Detach memory buffer only when GrowMemory is called from the JS API

test/mjsunit/regress/wasm/regression-699485.js

+// Copyright 2016 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --expose-wasm
+
+load("test/mjsunit/wasm/wasm-constants.js");
+load("test/mjsunit/wasm/wasm-module-builder.js");
+
+(function() {
+"use asm";
+var builder = new WasmModuleBuilder();
+builder.addMemory(0, 5, false);
+builder.addFunction("regression_699485", kSig_i_v)
+  .addBody([
+      kExprI32Const, 0x04,
+      kExprNop,
+      kExprGrowMemory, 0x00,
+      ]).exportFunc();
+let module = builder.instantiate();
+assertEquals(0, module.exports.regression_699485());
+})();