On a database where many modules are installed (e.g. runbot all), with
the option "manage available packaging options per products", doing a groupby
"product" on the "package type" list view triggers a js error.
It comes from the fact that the fixed_group variable contains a "length"
attribute; the _().each function uses this to determine (erroneously)
that the object is an array.
It thus uses fixed_group[0] to get an undefined, and then tries to access
a method of undefined.
We replace the each by a simple js loop.
opw 1863576