Fix stack buffer overflow WRITE 1 in domain_to_punycode()

Reported-by: oss-fuzz (issue 39424 and issue 39226)

The affected code would only be built into the library when
configured to build without any IDNA library.

src/psl.c

@@ -590,7 +590,7 @@ static int domain_to_punycode(const char *domain, char *out, size_t outsize)
 			memcpy(out + outlen, "xn--", 4);
 			outlen += 4;
 
-			labellen = outsize - outlen - 1; // -1 to leave space for the trailing \0
+			labellen = outsize - outlen - (e != NULL) - 1; // -1 to leave space for the trailing \0
 			if (punycode_encode(inputlen, input, &labellen, out + outlen))
 				return 1;
 			outlen += labellen;