Undefined index in badges/renderer.php (take#2)

This may be considered a followup/take#2 of MDL-64441 where a similar PHP notice was fixed. sarjona pointed me to that issue.

Using recent 38_STABLE (3.8.1 release), when displaying badge details... if the badge is missing any language... it shows:

Notice: Undefined index: in .../moodle_ci_site/badges/renderer.php on line 176

For badges in the same site but with a language, no notice is shown.

Ciao

(added 37, 38 and 39 as versions though I've not verified it against 37)