Fix config-panel switching on GTK 1.

When I reworked the 'selparams' array in commit e790adec4 to contain
pointers to 'struct selparam' rather than directly containing
structures, I missed this one case where I should have removed an &.
As a result the GTK1 signal handler that deals with clicks on the
config-pane selection treeview was getting a pointer to a pointer and
treating it as a pointer to an object. Nothing good happened.

unix/gtkdlg.c

@@ -3192,7 +3192,7 @@ GtkWidget *create_config_box(const char *title, Conf *conf,
     for (index = 0; index < nselparams; index++) {
         g_signal_connect(G_OBJECT(selparams[index]->treeitem), "select",
                          G_CALLBACK(treeitem_sel),
-                         &selparams[index]);
+                         selparams[index]);
         dp->treeitems[index] = selparams[index]->treeitem;
     }
 #endif