mfplat: Handle null destination for GetItem().

dlls/mfplat/main.c

@@ -1112,7 +1112,7 @@ HRESULT attributes_GetItem(struct attributes *attributes, REFGUID key, PROPVARIA
     EnterCriticalSection(&attributes->cs);
 
     if ((attribute = attributes_find_item(attributes, key, NULL)))
-        hr = PropVariantCopy(value, &attribute->value);
+        hr = value ? PropVariantCopy(value, &attribute->value) : S_OK;
     else
         hr = MF_E_ATTRIBUTENOTFOUND;
 

dlls/mfplat/tests/mfplat.c

@@ -763,6 +763,12 @@ static void test_attributes(void)
     PropVariantClear(&ret_propvar);
     CHECK_ATTR_COUNT(attributes, 1);
 
+    hr = IMFAttributes_GetItem(attributes, &DUMMY_GUID1, NULL);
+    ok(hr == S_OK, "Item check failed, hr %#x.\n", hr);
+
+    hr = IMFAttributes_GetItem(attributes, &DUMMY_GUID2, NULL);
+    ok(hr == MF_E_ATTRIBUTENOTFOUND, "Unexpected hr %#x.\n", hr);
+
     PropVariantInit(&ret_propvar);
     ret_propvar.vt = MF_ATTRIBUTE_STRING;
     U(ret_propvar).pwszVal = NULL;