GetFInfo: initialize ioFRefNum

[jepler]

According to Inside Macintosh Volume (IV-148/149) this field must be set to 0 in order to use the name in ioNamePtr.

In my project I noticed that GetFInfo was unreliable. I think this is the cause.

Note: This is not the fix I'm using locally. I actually am using this:

static OSErr GetFInfo_fixed(ConstStr255Param fileName, short vRefNum,
    FInfo *fndrInfo) {
    ParamBlockRec pb = {
        .fileParam.ioVRefNum = vRefNum,
        .fileParam.ioNamePtr = (StringPtr)fileName,
    };
    OSErr err;
    err = PBGetFInfoSync(&pb);
    *fndrInfo = pb.fileParam.ioFlFndrInfo;
    return err;
}

That style of initialization causes ALL other fields to be zero-initialized, according to my understanding of C. However, it may be less compatible with older compilers and/or generate more code.