Fix 208952f: incorrect truncation in string setting validation

(cherry picked from commit f2a8e18792)

src/settings.cpp

@@ -690,7 +690,7 @@ void StringSettingDesc::MakeValueValid(std::string &str) const
 	/* In case a maximum length is imposed by the setting, the length
 	 * includes the '\0' termination for network transfer purposes.
 	 * Also ensure the string is valid after chopping of some bytes. */
-	std::string stdstr(str, this->max_length - 1);
+	std::string stdstr(str, 0, this->max_length - 1);
 	str.assign(StrMakeValid(stdstr, SVS_NONE));
 }