Fix #72278: getimagesize returning FALSE on valid jpg

Fix #72278: getimagesize returning FALSE on valid jpg

getimagesize() is rather strict about the length of the marker payload data,
and fails if there are extraneous bytes before the next marker. Only a very
special case reported in bug #13213 is catered to.

libjpeg is rather resilient to such corrupted JPEG files, and raises a
recoverable error in this case. Other image processors also accept such
JPEG files, so we adapt getimagesize() to skip (but warn about) such
extraneous bytes.