Author: Ankit Agarwal
MDL-55762 assignpdf: Handle errored pages better
http://git.moodle.org/gw?p=moodle.git;a=commit;h=7b14fef5277ae611e3b91d4a6619dcba0b1922b6
http://github.com/moodle/moodle/commit/7b14fef5277ae611e3b91d4a6619dcba0b1922b6
+ 3.1 en [errorpdfpage,assignfeedback_editpdf]