Global search does not currently find any results when searching as a guest user, even if the guest user has access to the content.

(This is reproducible on qa.moodle.net)

Steps to reproduce:
You need a course with some content. (I used the activities example course on qa.moodle.net)
1. Log in as a teacher and navigate to your course
2. Enable guest access to the course (via Users -> enrollment methods)
3. Perform a search for some content within the course and make sure you get some results (book and resource activities work best here)
4. Make a note of your search results
5. Log out of moodle
6. Log in as a guest.
7. Navigate to the same course you visited in step 1
8. Perform the same search you performed in step 3
Expected results: You should get some search results
Actual results: No results found