Don't generate empty SQL commands if no data is to be changed.

ocdb.cpp

@@ -164,6 +164,9 @@ bool OCdb::update_cache(json j) {
 	if (j["data"]["owner"].count("uuid") > 0 && !j["data"]["owner"]["uuid"].is_null())
 		fields["owner"] = j["data"]["owner"]["uuid"].get<std::string>();
 
+	if (fields.empty() && fields2.empty())
+		return 2;
+
 	std::string sql = "INSERT INTO caches (code,";
 	for (auto& i : fields)
 		sql += i.first + ',';
@@ -220,6 +223,9 @@ bool OCdb::update_log(json j) {
 	if (j["data"].count("text") > 0 && !j["data"]["text"].is_null())
 		fields["text"] = j["data"]["text"].get<std::string>();
 
+	if (fields.empty())
+		return 2;
+
 	std::string sql = "INSERT INTO logs (uuid,";
 	for (auto& i : fields)
 		sql += i.first + ',';