Update CCEditBoxImplIOS.mm

1. By executing 314: _systemControl = [[CCEditBoxImplIOS_objc alloc] initWithFrame:rect editBox:this];
2. We entered to the function 67: -(id) initWithFrame: (CGRect) frameRect editBox: (void*) editBox
3. Then 69: "self = [super init];" returns object with +1 retain count
4. 93: "return nil" Potential leak of an object stored into "self".