php: Uninitialized read in exif_process_IFD_in_MAKERNOTE

An issue was discovered in the EXIF component in PHP before 7.1.27, 7.2.x before 7.2.16, and 7.3.x before 7.3.3. There is an uninitialized read in exifprocessIFDinMAKERNOTE because of mishandling the datalen variable...