[FIX] translate.py: fallback on base lang if noterm

When there is a language and its base language translation files in a
module, in 12.0 an empty translation in the language translation file
will not fallback on the base language.

eg.

 fr.po : {'one': 'un', 'seventy': 'soixante-dix'}
 fr_BE.po: {'one': '', 'seventy': 'septante'}

 => the translation in fr_BE will be {'one': '', 'seventy': 'septante'}

 but before 7288b477 it would have been {'one': 'un', 'seventy': 'septante'}

With this commit, an empty translation is no longer created so does not
override base language.

Also the intention of d84b795b that was also lost is restored by
upserting only noupdate==false translation, and inserting the other
ones.

opw-1904638
closes #28297