bpo-42866: Fix refleak in CJK getcodec() (GH-24165)

Fix a reference leak in the getcodec() function of CJK codecs.

Author: vstinner

Misc/NEWS.d/next/Library/2021-01-08-10-57-21.bpo-42866.Y1DnrO.rst

@@ -0,0 +1,2 @@
+Fix a reference leak in the ``getcodec()`` function of CJK codecs. Patch by
+Victor Stinner.

Modules/cjkcodecs/cjkcodecs.h

@@ -291,6 +291,7 @@ getcodec(PyObject *self, PyObject *encoding)
 
     r = PyObject_CallOneArg(cofunc, codecobj);
     Py_DECREF(codecobj);
+    Py_DECREF(cofunc);
 
     return r;
 }