Fix libvncserver GnuTLS init.

gnutls_certificate_set_x509_trust_file() returns the number of processed
certs and _not_ GNUTLS_E_SUCCESS (0) on success!

libvncserver/rfbssl_gnutls.c

@@ -95,7 +95,7 @@ struct rfbssl_ctx *rfbssl_init_global(char *key, char *cert)
 	/* */
     } else if (!GNUTLS_E_SUCCESS == (ret = gnutls_certificate_allocate_credentials(&ctx->x509_cred))) {
 	/* */
-    } else if (!GNUTLS_E_SUCCESS == (ret = gnutls_certificate_set_x509_trust_file(ctx->x509_cred, cert, GNUTLS_X509_FMT_PEM))) {
+    } else if ((ret = gnutls_certificate_set_x509_trust_file(ctx->x509_cred, cert, GNUTLS_X509_FMT_PEM)) < 0) {
 	/* */
     } else if (!GNUTLS_E_SUCCESS == (ret = gnutls_certificate_set_x509_key_file(ctx->x509_cred, cert, key, GNUTLS_X509_FMT_PEM))) {
 	/* */