[wasm] Fix DCHECK handiling pending exceptions.

test/mjsunit/regress/wasm/regress-712569.js

+// Copyright 2017 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.
+//
+
+var v11 = {};
+Object.defineProperty(v11.__proto__, 0, {
+  get: function() {
+  },
+  set: function() {
+    try {
+      WebAssembly.instantiate();
+      v11[0] = 0;
+    } catch (e) {
+      assertTrue(e instanceof RangeError);
+    }
+  }
+});
+v66 = new Array();
+cv = v66; cv[0] = 0.1; cv[2] = 0.2;