s4:web_server: Fix build error

source4/web_server/wsgi.c:149:8: error: assignment discards 'const'
qualifier from pointer target type [-Werror=discarded-qualifiers]
    str = PyStr_AsUTF8AndSize(item, &size);
            ^

Signed-off-by: Andreas Schneider <[email protected]>
Reviewed-by: David Disseldorp <[email protected]>

Autobuild-User(master): Andreas Schneider <[email protected]>
Autobuild-Date(master): Tue Dec 11 13:58:30 CET 2018 on sn-devel-144

source4/web_server/wsgi.c

@@ -143,7 +143,7 @@ static PyObject *py_error_writelines(PyObject *self, PyObject *args, PyObject *k
 	}
 
 	while ((item = PyIter_Next(seq))) {
-		char *str = NULL;
+		const char *str = NULL;
 		Py_ssize_t size = 0;
 		if (!IsPy3Bytes(item)) {
 			str = PyStr_AsUTF8AndSize(item, &size);