Fix missing exception check in typed array constructor.

Fix missing exception check in typed array constructor.

The typed array constructor might fail if the first argument is an
object with a length property. Accessing the property can cause an
exception to be thrown and an explicit check needs to be performed.

R=verwaest@chromium.org
BUG=chromium:168545
TEST=mjsunit/regress/regress-crbug-168545.js

Committed: http://code.google.com/p/v8/source/detail?r=13325

[Toon Verwaest, 2013-01-07 13:50:07]

LGTM. Copying the elements is still broken though:
var o = [1,2,3];
Object.defineProperty(o, "1", { get: function() { throw "bail"; }});
new Int16Array(o);

[Michael Starzinger, 2013-01-07 13:55:33]

You are right, nice catch. I'll tackle that in a separate CL though.