return 'def' on the empty string again

src/serialization/string_utils.cpp

@@ -394,6 +394,7 @@ std::string &unescape(std::string &str)
 }
 
 bool string_bool(const std::string& str, bool def) {
+	if (str.empty()) return def;
 	if (str == "yes" || str == "on" || str == "true"
 	|| lexical_cast_default<int>(str), 0) {
 		return true;