Notification of string changes

Author: Matt Porritt
MDL-78048 Site Registration: Course Dates
Course date registration data reports correctly.

MDL-77306 added a count of how many courses there are
without start and end dates. However, all courses have
a start date, it is only the end date that is optional.
This patch fixes the data collection and makes the lang
string describing it clearer.


http://git.moodle.org/gw?p=moodle.git;a=commit;h=b87a75110bb929ce185fa83a7e6c2cda296b8483
http://github.com/moodle/moodle/commit/b87a75110bb929ce185fa83a7e6c2cda296b8483

+ 4.2 en [coursesnodates,core_hub]