Jpeg image plugin can not read some jpeg files without exif infomation.

the jpeg image format plugin can not read jpg file without exif info or without exif orientation info. refer to the attachment.

The problem is:
1, in bool QJpegHandlerPrivate::read(QImage *image)
Only if "State==ReadHeader', then it will read the jpeg contents.

But
2, in bool QJpegHandlerPrivate::readJpegHeader(QIODevice *device)

if (exifOrientation == -1)
return false;

At that time, even if the file is a valid jpg, if it does not contain any exif infos or does not contain exifOrientation infos, it will retrun directly and leave "state" not set to "ReadHeader".

Here is a patch to fix it:
diff -Nur qtbase-opensource-src-5.5.0/src/gui/image/qjpeghandler.cpp qtbase-opensource-src-5.5.0n/src/gui/image/qjpeghandler.cpp
— qtbase-opensource-src-5.5.0/src/gui/image/qjpeghandler.cpp 2015-06-29 20:04:51.000000000 +0000
+++ qtbase-opensource-src-5.5.0n/src/gui/image/qjpeghandler.cpp 2015-08-13 20:41:32.187145848 +0000
@@ -900,7 +900,8 @@
size = QSize(width, height);

format = QImage::Format_Invalid;

• read_jpeg_format(format, &info);
  + if(read_jpeg_format(format, &info))
  + state = ReadHeader;

QByteArray exifData;

@@ -935,7 +936,6 @@
transformation = exif2Qt(exifOrientation);
}

• state = ReadHeader;
  return true;
  }
  else

if "file is a valid jpg file" and be supported, then set "state" to "ReadHeader".

And the jpeghandler codes still need more improvements, for example:
"readJpegHeader" had a "bool' retrun value but the value is never used.

Actually, the existence and use of "ReadHeader" state is awkward and almost useless.