support BITMAPV5HEADER in getimagesize()

the php function getimagesize() doesn't support Bitmaps with ICC color profiles (BITMAPV5HEADER).
The size information is at the same position as Bitmaps with a BITMAPV4HEADER, so just adding a check for the different header size should be enough
https://en.wikipedia.org/wiki/BMP_file_format#DIB_header_.28bitmap_information_header.29