closed #4383: Fixed missing letters if using old LabelTTF and running on  iPhone 64bit simulator(device).

The return value of `_calculateStringSize` should be integer value.

```c++
dim.width = ceilf(dim.width);
dim.height = ceilf(dim.height);
return dim;
```

IOS7 64bit SDK seems to check whether string could be `drawInRect`, if it couldn't, there will not be any error  informations.

WHY doesn't `drawInRect` have return value? FUCK  IOS7.