Bugfix: using Image.GetCurrent() and image.save() on the "Render Result"
image could result in a segfault since image->ibuf was NULL. This change
forces ibuf to be created if necessary.
NOTE: the Image API needs additional methods/attributes for image.save() to
really do anything useful. The image type, quality, etc., don't seem to be
gettable/settable so the resulting image file may not be in the format the
user would like.
e194ccce5e