res_config_ldap: Fix erroneous LDAP_MOD_REPLACE in LDAP modify

We always treat the first change of our modification batch as a
replacement when it sometimes is actually a delete. So we have to pass
the correct arguments to the OpenLDAP library.

ASTERISK-26580 #close
Reported by: Nicholas John Koch
Patches:
	res_config_ldap.c-11.24.1.patch (license #6833) patch uploaded
	by Nicholas John Koch

Change-Id: I0741d25de07c9539f1edc6eff3696165dfb64fbe

res/res_config_ldap.c

@@ -1294,12 +1294,15 @@ static int update_ldap(const char *basedn, const char *table_name, const char *a
 	mods_size = 2; /* one for the first param/value pair and one for the the terminating NULL */
 	ldap_mods = ldap_memcalloc(sizeof(LDAPMod *), mods_size);
 	ldap_mods[0] = ldap_memcalloc(1, sizeof(LDAPMod));
-
-	ldap_mods[0]->mod_op = LDAP_MOD_REPLACE;
 	ldap_mods[0]->mod_type = ldap_strdup(newparam);
 
-	ldap_mods[0]->mod_values = ast_calloc(sizeof(char *), 2);
+	if (strlen(field->value) == 0) {
-	ldap_mods[0]->mod_values[0] = ldap_strdup(field->value);
+		ldap_mods[0]->mod_op = LDAP_MOD_DELETE;
+	} else {
+		ldap_mods[0]->mod_op = LDAP_MOD_REPLACE;
+		ldap_mods[0]->mod_values = ast_calloc(sizeof(char *), 2);
+		ldap_mods[0]->mod_values[0] = ldap_strdup(field->value);
+	}
 
 	while ((field = field->next)) {
 		newparam = convert_attribute_name_to_ldap(table_config, field->name);