[FIX] web: properly apply onchange in some cases

A previous commit (8dbd1efe) fixed a
part of the basicmodel that used _.each to iterate on an object with
field names as keys, which does not work when a field is named "length".
To fix it, I simply used a native for ... in statement.  However, I
missed the fact that there was a second 'return' statement in the body
of the closure given to _.each, so the onchange method returned
prematurely.

The fix is to simply use the continue statement in that case.

closes odoo/odoo#67228

Signed-off-by: Aaron Bohy (aab) <aab@odoo.com>