lib-fts: Minor fix to randomness test in test-fts-tokenizer

If the random input was entirely valid UTF-8, the input was truncated to
empty.

src/lib-fts/test-fts-tokenizer.c

@@ -490,7 +490,8 @@ static void test_fts_tokenizer_random(void)
 		for (unsigned int j = 0; j < sizeof(addr); j++)
 			addr[j] = test_chars[i_rand() % N_ELEMENTS(test_chars)];
 		str_truncate(str, 0);
-		(void)uni_utf8_get_valid_data(addr, sizeof(addr), str);
+		if (uni_utf8_get_valid_data(addr, sizeof(addr), str))
+			str_append_data(str, addr, sizeof(addr));
 		while (fts_tokenizer_next(tok, str_data(str), str_len(str),
 					  &token, &error) > 0) ;
 		while (fts_tokenizer_final(tok, &token, &error) > 0) ;