minor bug in CCImage_ios.mm

cocos2d-x C++
#1

in _caculateStringSizeWithFontOrZFont():

tmp = [FontLabelStringDrawingHelper sizeWithZFont:str zfont:font constrainedToSize:textRect];

should be

tmp = [FontLabelStringDrawingHelper sizeWithZFont:s zfont:font constrainedToSize:textRect];
#2

mark

#3

Thank you.
#1230 is created for it.