Blender Git Loki

Serious bugfix for compositing; using Groups could crash if one of the
input nodes was 'passing on' the buffer (because it didn't operate on the
image). That's for example for Blur with size 0 or for Translate node.
This passed-on buffer then got freed inside the group...

Solution now is just a malloc. Better system should be devised, with
reference counting or so. Thanks Ivan Hoffmann for the sample file!