Fix closing reconnect dialog logic

If you close the reconnect dialog then we should assume that you want to
close things, not that you want to reconnect. Unfortunately FLTK returns
the first choice when closing the dialog, so that needs to be the
"Cancel" alternative.

vncviewer/vncviewer.cxx

       int ret;
       ret = fl_choice(_("%s\n\n"
                         "Attempt to reconnect?"),
-                      fl_yes, fl_no, 0, exitError);
+                      NULL, fl_yes, fl_no, exitError);
       free(exitError);
       exitError = NULL;
-      if (ret == 0)
+      if (ret == 1)
         continue;
       else
         break;