Please describe the problem:
When invoked from the python console, the procedure pdb.plug_in_gap_morph_layers can successfully create at most 3 tweening frames. Requesting 4 or more tweening frames causes the plugin to crash with a segfault.

Steps to reproduce:
1. Create a new image
2. Make two transparency layers with different contents
3. Open the python-fu console
4. Execute 
pdb.plug_in_gap_morph_layers(gimp.image_list()[0], gimp.image_list()[0].layers[1], gimp.image_list()[0].layers[2], 4, 0, True, "/home/aniket/research/morph/workfile", "/home/aniket/research/morph/workfile");
This requests four tweening frames and reveals the bug.

Actual results:
Only three tweening are created of the four expected. A cluttered image is also created and available in the images window, representing some intermittent step of the morphing process. 

The python-fu console displays:
Traceback (most recent call last):

+ Trace 195315

The linux terminal from which gimp was executed console displays:
/usr/lib/gimp/2.0/plug-ins/gtkcons.py:186: GtkDeprecationWarning: gtk.idle_add is deprecated, use gobject.idle_add instead
  gtk.idle_add(self.focus_text)
/usr/lib/gimp/2.0/plug-ins/gap_morph: fatal error: Segmentation fault

Expected results:
Four tweening frames should be created

Does this happen every time?
Yes

Other information:
I have not been able to reproduce this problem using the GUI.

The plugin requires a work file to execute. I created this file using the GUI, and in my case all of the data points are along the border of the image, as is the default.