Validate config strings as UTF-8.

src/conf.c

@@ -2026,6 +2026,10 @@ static int conf__parse_string(char **token, const char *name, char **value, char
 		while((*token)[0] == ' ' || (*token)[0] == '\t'){
 			(*token)++;
 		}
+		if(mosquitto_validate_utf8(*token, strlen(*token))){
+			log__printf(NULL, MOSQ_LOG_ERR, "Error: Malformed UTF-8 in configuration.");
+			return MOSQ_ERR_INVAL;
+		}
 		*value = mosquitto__strdup(*token);
 		if(!*value){
 			log__printf(NULL, MOSQ_LOG_ERR, "Error: Out of memory.");