lib-sieve: Make static analyzer happier about use of sieve_ast_string…

…list_map().

Added assertions.

src/lib-sieve/ext-envelope.c

@@ -569,7 +569,7 @@ static bool tst_envelope_validate
 	epart = arg;
 	if ( sieve_ast_stringlist_map(&epart, (void *) &not_address,
 		_envelope_part_is_supported) <= 0 ) {
-
+		i_assert(epart != NULL);
 		sieve_argument_validate_error(valdtr, epart,
 			"specified envelope part '%s' is not supported by the envelope test",
 				str_sanitize(sieve_ast_strlist_strc(epart), 64));

src/lib-sieve/tst-address.c

@@ -167,6 +167,7 @@ static bool tst_address_validate
 	header = arg;
 	if ( sieve_ast_stringlist_map
 		(&header, NULL, _header_is_allowed) <= 0 ) {
+		i_assert(header != NULL);
 		sieve_argument_validate_error(valdtr, header,
 			"specified header '%s' is not allowed for the address test",
 			str_sanitize(sieve_ast_strlist_strc(header), 64));