jpegparse: Fix APP1 marker segment parsing

Reposition the bytereader for proper skipping of
APP1 marker segment if it is not Exif.

https://bugzilla.gnome.org/show_bug.cgi?id=795117
diff --git a/gst/jpegformat/gstjpegparse.c b/gst/jpegformat/gstjpegparse.c
index dd684d7..0bfdc80 100644
--- a/gst/jpegformat/gstjpegparse.c
+++ b/gst/jpegformat/gstjpegparse.c
@@ -572,6 +572,9 @@
         APP1, id_str, size);
 
   } else {
+    /* restore the byte position and size */
+    reader->size += 2;
+    reader->byte -= 2;
     if (!gst_jpeg_parse_skip_marker (parse, reader, APP1))
       return FALSE;
   }