uninitialized Ptr<CascadeClassifierImpl> ccimpl in bool CascadeClassifier::read(const FileNode &root) (Bugfix #3530)

sometimes it's nessecary to read a cascade file from memory.

the following code worked nicely in 2.4.2:

// simulate 'in memory' situation
    const char * path = "E:/code/opencv/data/haarcascades /haarcascade_eye.xml";
    FILE * f = fopen(path,"rb");
    char buf[0x8ffff];
    int r = fread(buf,1,0x8ffff,f);
    buf[r]=0;

// load it into CascadeClassifier:
    CascadeClassifier cf; 
    FileStorage fs(buf, FileStorage::READ | FileStorage::MEMORY);
    FileNode fn = fs.getFirstTopLevelNode();
    bool ok = cf.read(fn);

same code crashes with 3.0, due to uninitialized Ptr<CascadeClassifierImpl> ccimpl in bool CascadeClassifier::read(const FileNode &root)

changing the code to this:

bool CascadeClassifier::read(const FileNode &root)
{
        Ptr<CascadeClassifierImpl> ccimpl = makePtr<CascadeClassifierImpl>();
        bool ok = ccimpl->read_(root);

...

made it work for me ( but not sure, if that's the right fix, all a bit over my head, i have to say .. )