Exception opening attached files

[Marx1st]

Hi!

We've recently upgraded Moodleoverflow to v4.2-r1 2023052200 on our Moodle 3.11.14+ site.

After that files attached to posts can not be opended anymore (neither existing or newly added files).

The error:

`Exception - Call to a member function is_external_file() on bool

More information about this error
Debug info:
Error code: generalexceptionmessage
Stack trace:

line 2719 of /lib/filelib.php: Error thrown
line 465 of /mod/moodleoverflow/lib.php: call to send_stored_file()
line 5156 of /lib/filelib.php: call to moodleoverflow_pluginfile()
line 44 of /pluginfile.php: call to file_pluginfile()`

The problem did not exist with Moodleoverflow v4.1-r1 2022120600.

[NinaHerrmann]

Already mentioned in #144 and work in progress in #146

[NinaHerrmann]

There is a release fixing the issue (4.2-r2) :)