libgimp, plug-ins: let's just call gegl_init() in gimp_ui_init().

bootchk had the case in commit 6781a35668. I again had it with gfig. I think it
just makes sense to init GEGL, especially as the errors are not that explicit
and that the plug-in code may not even call GEGL code directly (so it makes it
harder to guess).

plug-ins/script-fu/libscriptfu/script-fu-interface.c

@@ -196,7 +196,6 @@ script_fu_interface (SFScript  *script,
   if (!gtk_initted)
     {
       gimp_ui_init ("script-fu");
-      gegl_init (NULL, NULL);
 
       gtk_initted = TRUE;
     }