Fix get_email: 0 is a valid return value

crypto/x509v3/v3_utl.c

@@ -492,7 +492,7 @@ static STACK *get_email(X509_NAME *name, GENERAL_NAMES *gens)
 	i = -1;
 	/* First supplied X509_NAME */
 	while((i = X509_NAME_get_index_by_NID(name,
-					 NID_pkcs9_emailAddress, i)) > 0) {
+					 NID_pkcs9_emailAddress, i)) >= 0) {
 		ne = X509_NAME_get_entry(name, i);
 		email = X509_NAME_ENTRY_get_data(ne);
 		if(!append_ia5(&ret, email)) return NULL;