OutputPage: Condition-wrap the <script> for 'user.groups'

OutputPage: Condition-wrap the <script> for 'user.groups'

Follows-up 9d390a09cdfb. It already wraps the only=script requests
for 'site' and 'user', but forgot about 'user.groups' which is
not 'scripts' but 'combined' (as regular module requests).

That request responds with mw.loader.implement whih will be absent
if the environment is unsupported.

With normal module requests, this is naturally covered by those
requests not being fired from mw.loader in the first place but
with hardcoded requests like these the condition wrap with
document.write is unfortunately required in the current reality.

Change-Id: Ib3a7378d0c44e601760fbbc5174da09bd7b7f492