psutil: Fix for CVE-2019-18874

giampaolo/psutil#1616
giampaolo/psutil@7d512c8

CVE fix commit message by Riccardo Schirone:
Use Py_CLEAR instead of Py_DECREF to also set the variable to NULL

These files contain loops that convert system data into python objects
and during the process they create objects and dereference their
refcounts after they have been added to the resulting list.

However, in case of errors during the creation of those python objects,
the refcount to previously allocated objects is dropped again with
Py_XDECREF, which should be a no-op in case the paramater is NULL. Even
so, in most of these loops the variables pointing to the objects are
never set to NULL, even after Py_DECREF is called at the end of the loop
iteration. This means, after the first iteration, if an error occurs
those python objects will get their refcount dropped two times,
resulting in a possible double-free.
 master (#1616)

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CVEs fixed in this build:
CVE-2019-18874