allow unsetting of tls_* syncrepl options

Author: Patrick Monnerat <pm@datasphere.ch>
Upstream ITS: #7042
Resolves: #734187

diff --git a/libraries/libldap/tls2.c b/libraries/libldap/tls2.c
index 654a4bf..10b993b 100644
--- a/libraries/libldap/tls2.c
+++ b/libraries/libldap/tls2.c
@@ -735,27 +735,27 @@ ldap_pvt_tls_set_option( LDAP *ld, int option, void *arg )
 		return 0;
 	case LDAP_OPT_X_TLS_CACERTFILE:
 		if ( lo->ldo_tls_cacertfile ) LDAP_FREE( lo->ldo_tls_cacertfile );
-		lo->ldo_tls_cacertfile = arg ? LDAP_STRDUP( (char *) arg ) : NULL;
+		lo->ldo_tls_cacertfile = (arg && *(char *)arg) ? LDAP_STRDUP( (char *) arg ) : NULL;
 		return 0;
 	case LDAP_OPT_X_TLS_CACERTDIR:
 		if ( lo->ldo_tls_cacertdir ) LDAP_FREE( lo->ldo_tls_cacertdir );
-		lo->ldo_tls_cacertdir = arg ? LDAP_STRDUP( (char *) arg ) : NULL;
+		lo->ldo_tls_cacertdir = (arg && *(char *)arg) ? LDAP_STRDUP( (char *) arg ) : NULL;
 		return 0;
 	case LDAP_OPT_X_TLS_CERTFILE:
 		if ( lo->ldo_tls_certfile ) LDAP_FREE( lo->ldo_tls_certfile );
-		lo->ldo_tls_certfile = arg ? LDAP_STRDUP( (char *) arg ) : NULL;
+		lo->ldo_tls_certfile = (arg && *(char *)arg) ? LDAP_STRDUP( (char *) arg ) : NULL;
 		return 0;
 	case LDAP_OPT_X_TLS_KEYFILE:
 		if ( lo->ldo_tls_keyfile ) LDAP_FREE( lo->ldo_tls_keyfile );
-		lo->ldo_tls_keyfile = arg ? LDAP_STRDUP( (char *) arg ) : NULL;
+		lo->ldo_tls_keyfile = (arg && *(char *)arg) ? LDAP_STRDUP( (char *) arg ) : NULL;
 		return 0;
 	case LDAP_OPT_X_TLS_DHFILE:
 		if ( lo->ldo_tls_dhfile ) LDAP_FREE( lo->ldo_tls_dhfile );
-		lo->ldo_tls_dhfile = arg ? LDAP_STRDUP( (char *) arg ) : NULL;
+		lo->ldo_tls_dhfile = (arg && *(char *)arg) ? LDAP_STRDUP( (char *) arg ) : NULL;
 		return 0;
 	case LDAP_OPT_X_TLS_CRLFILE:	/* GnuTLS only */
 		if ( lo->ldo_tls_crlfile ) LDAP_FREE( lo->ldo_tls_crlfile );
-		lo->ldo_tls_crlfile = arg ? LDAP_STRDUP( (char *) arg ) : NULL;
+		lo->ldo_tls_crlfile = (arg && *(char *)arg) ? LDAP_STRDUP( (char *) arg ) : NULL;
 		return 0;
 	case LDAP_OPT_X_TLS_REQUIRE_CERT:
 		if ( !arg ) return -1;
@@ -783,7 +783,7 @@ ldap_pvt_tls_set_option( LDAP *ld, int option, void *arg )
 #endif
 	case LDAP_OPT_X_TLS_CIPHER_SUITE:
 		if ( lo->ldo_tls_ciphersuite ) LDAP_FREE( lo->ldo_tls_ciphersuite );
-		lo->ldo_tls_ciphersuite = arg ? LDAP_STRDUP( (char *) arg ) : NULL;
+		lo->ldo_tls_ciphersuite = (arg && *(char *)arg) ? LDAP_STRDUP( (char *) arg ) : NULL;
 		return 0;
 
 	case LDAP_OPT_X_TLS_PROTOCOL_MIN:
@@ -794,7 +794,7 @@ ldap_pvt_tls_set_option( LDAP *ld, int option, void *arg )
 		if ( ld != NULL )
 			return -1;
 		if ( lo->ldo_tls_randfile ) LDAP_FREE (lo->ldo_tls_randfile );
-		lo->ldo_tls_randfile = arg ? LDAP_STRDUP( (char *) arg ) : NULL;
+		lo->ldo_tls_randfile = (arg && *(char *)arg) ? LDAP_STRDUP( (char *) arg ) : NULL;
 		break;
 	case LDAP_OPT_X_TLS_NEWCTX:
 		if ( !arg ) return -1;