patch 8.0.1283: test 86 fails under ASAN

Problem:    Test 86 fails under ASAN.
Solution:   Fix that an item was added to a dictionary twice.

Author: brammool

src/if_py_both.h

@@ -1996,6 +1996,7 @@ DictionaryUpdate(DictionaryObject *self, PyObject *args, PyObject *kwargs)
 		PyObject	*todecref;
 		char_u		*key;
 		dictitem_T	*di;
+		hashitem_T	*hi;
 
 		if (!(fast = PySequence_Fast(item, "")))
 		{
@@ -2052,7 +2053,8 @@ DictionaryUpdate(DictionaryObject *self, PyObject *args, PyObject *kwargs)
 
 		Py_DECREF(fast);
 
-		if (dict_add(dict, di) == FAIL)
+		hi = hash_find(&dict->dv_hashtab, di->di_key);
+		if (!HASHITEM_EMPTY(hi) || dict_add(dict, di) == FAIL)
 		{
 		    RAISE_KEY_ADD_FAIL(di->di_key);
 		    Py_DECREF(iterator);

src/version.c

@@ -761,6 +761,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1283,
 /**/
     1282,
 /**/