fix: make remove-torrent dialogs modal in GTK client (#2602)

Followup to #2443

gtk/Dialogs.cc

@@ -101,10 +101,10 @@ void gtr_confirm_remove(
     auto d = std::make_shared<Gtk::MessageDialog>(
         parent,
         gtr_sprintf("<big><b>%s</b></big>", primary_text),
-        true,
+        true /*use_markup*/,
         Gtk::MESSAGE_QUESTION,
         Gtk::BUTTONS_NONE,
-        false);
+        true /*modal*/);
 
     if (!secondary_text.empty())
     {

gtk/Utils.cc

@@ -516,9 +516,10 @@ void gtr_unrecognized_url_dialog(Gtk::Widget& parent, Glib::ustring const& url)
     auto w = std::make_shared<Gtk::MessageDialog>(
         *window,
         _("Unrecognized URL"),
-        false,
+        false /*use markup*/,
         Gtk::MESSAGE_ERROR,
-        Gtk::BUTTONS_CLOSE);
+        Gtk::BUTTONS_CLOSE,
+        true /*modal*/);
 
     gstr += gtr_sprintf(_("Transmission doesn't know how to use \"%s\""), url);