MDL-36881 Handle poorly behaved modname_get_types functions better
The modname_get_types function is not always well implemented by
third-party plugins and some return poor data. This in turn leads to
incorrect module definitions, and can lead to problems in both the
'Add an activity...' dropdowns and the Activity chooser.
This will also prevent display of plugins which legitimately can have
subtypes but where no subtypes were found. Since such plugins cannot be
used in this fashion in any case, this is also beneficial.
Signed-off-by: Andrew Robert Nicols <andrew.nicols@lancaster.ac.uk>
