user32: Return DMLERR_INVALIDPARAMETER if hszItem is NULL.

dlls/user32/dde_client.c

@@ -1163,7 +1163,7 @@ HDDEDATA WINAPI DdeClientTransaction(LPBYTE pData, DWORD cbData, HCONV hConv, HS
 	pXAct = WDML_ClientQueueUnadvise(pConv, wFmt, hszItem);
 	break;
     case XTYP_REQUEST:
-	if (pData)
+	if (pData || !hszItem)
 	{
 	    pConv->instance->lastError = DMLERR_INVALIDPARAMETER;
             return 0;

dlls/user32/tests/dde.c

@@ -353,10 +353,7 @@ static void test_ddeml_client(void)
     ret = DdeGetLastError(client_pid);
     ok(hdata == NULL, "Expected NULL hdata, got %p\n", hdata);
     ok(res == 0xdeadbeef, "Expected 0xdeadbeef, got %08x\n", res);
-    todo_wine
-    {
-        ok(ret == DMLERR_INVALIDPARAMETER, "Expected DMLERR_INVALIDPARAMETER, got %d\n", ret);
-    }
+    ok(ret == DMLERR_INVALIDPARAMETER, "Expected DMLERR_INVALIDPARAMETER, got %d\n", ret);
 
     DdeFreeStringHandle(client_pid, item);