Since --convert isn't mandatory anymore for --outformat to be used
(what was conflicting with --mutt-query), we removed the call to
set_convert_var() in 
141acfcc.
We now need to test that one of MODE_CONVERT and MODE_QUERY is 'on'
before allowing the use of --outformat.
$ abook --outformat anyformat < file	# won't hang anymore
 
                                set_convert_var(informat);
                                break;
                        case OPT_OUTFORMAT:
+                               if(mode != MODE_CONVERT && mode != MODE_QUERY) {
+                                 fprintf(stderr,
+                                         _("please use option --outformat after --convert or --mutt-query option\n"));
+                                 exit(EXIT_FAILURE);
+                               }
                                // ascii-name is stored, it's used to traverse
                                // e_filters[] in MODE_CONVERT (see export_file())
                                outformat = optarg;