Add missing string length check in regexp engine.

test/mjsunit/regress/regress-2172.js

Index: test/mjsunit/regress/regress-2172.js
diff --git a/test/mjsunit/regress/regress-crbug-126414.js b/test/mjsunit/regress/regress-2172.js
similarity index 92%
copy from test/mjsunit/regress/regress-crbug-126414.js
copy to test/mjsunit/regress/regress-2172.js
index 6674267d74d386f5434cb51935cb76a7c84c5734..5d06f4eef459efbf37c42d087db7ad0cb0c3a09f 100644
--- a/test/mjsunit/regress/regress-crbug-126414.js
+++ b/test/mjsunit/regress/regress-2172.js
@@ -25,8 +25,11 @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-function foo(bar)  {
-  return arguments[bar];
+for (var i = 0; i < 10000; i++){
+  (i + "\0").split(/(.)\1/i);
 }
-foo(0);           // Handled in runtime.
-foo(-536870912);  // Triggers bug.
+
+for (var i = 0; i < 10000; i++){
+  (i + "\u1234\0").split(/(.)\1/i);
+}
+