gtktextview.c/gtk_text_view_backspace() around line 5167:

      attrs = _gtk_text_buffer_get_line_log_attrs (get_buffer
(text_view), &insert, NULL);
      offset = gtk_text_iter_get_line_offset (&insert);
      backspace_deletes_character =
attrs[offset].backspace_deletes_character;

Ok, so if attrs == NULL, then attempting to do attrs[offset] will of
course segfault.

So, we look at _gtk_text_buffer_get_line_log_attrs():
  gint line;
  GtkTextLogAttrCache *cache;
  gint i;
    
  g_return_val_if_fail (GTK_IS_TEXT_BUFFER (buffer), NULL);
  g_return_val_if_fail (anywhere_in_line != NULL, NULL);
    
  /* special-case for empty last line in buffer */
  if (gtk_text_iter_is_end (anywhere_in_line) &&
      gtk_text_iter_get_line_offset (anywhere_in_line) == 0)
    {
      if (char_len)
        *char_len = 0;
      return NULL;
    }
    
Hmm, NULL seems to be a valid return value for this function, which
would cause gtk_text_view_backspace() to get an attrs==NULL.

Test was:
1) run gedit
2) hit Enter
3) Hit backspace