When an error is returned, the client crashes as EndModal is called twice.

This fixes that and simply returns instead.  At least GTK won't complain.

ui.cpp

@@ -1952,6 +1952,7 @@ void CSendDialog::OnButtonSend(wxCommandEvent& event)
                 {
                     wxMessageBox(strError + "  ", _("Sending..."));
                     EndModal(false);
+                    return;
                 }
 	    }
         }