title: Objective c ccTouchesBegan issue
body: <p>i have a problem with ccTouchesBegan</p>
  
  <p><pre>  <code>
  - (void)ccTouchesBegan:(UITouch *)touches withEvent:(UIEvent *)event {
  if (_mouseJoint != NULL) return;
  _paddleBody=body2;
  UITouch *myTouch = [touches anyObject];
  CGPoint location = [myTouch locationInView:[myTouch view]];
  location = [[CCDirector sharedDirector] convertToGL:location];
  b2Vec2 locationWorld = b2Vec2(location.x/PTM_RATIO, location.y/PTM_RATIO);
  if (_paddleFixture->TestPoint(locationWorld)) {
  b2MouseJointDef md;
  md.bodyA = groundBody;
  md.bodyB = _paddleBody;
  md.target = locationWorld;
  md.collideConnected = true;
  md.maxForce = 1000.0f * _paddleBody->GetMass();
  _mouseJoint = (b2MouseJoint *)_world->CreateJoint(&amp;md);
  _paddleBody->SetAwake(true);
  }
  }
  </pre></code>
  on the line
  <pre><code>location = [[CCDirector sharedDirector] convertToGL:location];</pre></code>
  i have such error
  <pre><code>
  (gdb) continue
  Program received signal: “EXC_BAD_ACCESS”.
  Previous frame inner to this frame (gdb could not unwind past this frame)
  Previous frame inner to this frame (gdb could not unwind past this frame)
  </pre></code>
  and i do not get the reasone why
  Help me, please</p>