jpeg: Increase memory limit for loading image data
jpeg: Increase memory limit for loading image data

As fix for security issue #205 when loading image data the memory size
was limited to 100 MB. That seemed like a good threshold. For larger
images, from around 18 megapixels (MP) and up though not for all such
images, this threshold was too low. Increasing the threshold too 300 MB
seems to work better and lets larger images load.

Fixes #216.
GNOME/gdk-pixbuf,GNOME/gdk-pixbuf,GNOME/gdk-pixbuf,GNOME/gdk-pixbuf