Author: Nelson Moller
MDL-51090: mod_quiz grading validation of an essay question
An invalid format is casted to 0 (if a string) or to some truncated value in other cases (ex: 10..5).
http://git.moodle.org/gw?p=moodle.git;a=commit;h=9f3a76cb07ef1137d151af9227e78fa0a72a68cf
http://github.com/moodle/moodle/commit/9f3a76cb07ef1137d151af9227e78fa0a72a68cf
+ 2.9 en [manualgradeinvalidformat,core_question]