[IMP] tools: fallback on empty translation

Avoid returning False if, for any reason, the return is falsy (False,
None,...)

Following the discussion in odoo/odoo#53254, the root cause was a call in the form
  _(foo)

where foo was equal False

While nothing else than a string should be the argument of _, it's
still technically possible to pass something else and get a bad return
value.
Fallback on empty string to be consistent.

odoo/tools/translate.py

@@ -487,7 +487,7 @@ class GettextAlias(object):
         finally:
             if cr and is_new_cr:
                 cr.close()
-        return res
+        return res or ''
 
 
 @functools.total_ordering