When sending a message to multiple participants in a course, line breaks disappear.

To reproduce the issue:

• Prepare a course with a teacher and a test student
• As the teacher, go to the course (e.g. /course/view.php?id=...)
• Under the navigation block, press "Participants"
• In the table, tick the test student, and select "send message" in the "With selected users..."-dropdown
• Enter a message containing linebreaks. (Could be "Dear Students,\nText goes here")
• Press "preview" followed by "send message"
• As the test student, read the message
• Observe that linebreaks in the message are missing: "Dear Students, Text goes here"

Note: This affects both linebreaks and new paragraphs.