Here's the upstream patch formatted for debian/patches.
Chris
--- a/modules/webkit-editor/web-extension/e-editor-dom-functions.c +++ b/modules/webkit-editor/web-extension/e-editor-dom-functions.c @@ -8421,7 +8421,7 @@ change_cid_images_src_to_base64 (EEditor list = webkit_dom_document_query_selector_all ( document, selector, NULL); - for (jj = webkit_dom_node_list_get_length (list) - 1; jj--;) { + for (jj = webkit_dom_node_list_get_length (list); jj--;) { WebKitDOMNode *node = webkit_dom_node_list_item (list, jj); set_base64_to_element_attribute (