user32: DdeClientTransaction should check that pData is not NULL for XTYP_REQUEST.

dlls/user32/dde_client.c

@@ -1154,6 +1154,11 @@ HDDEDATA WINAPI DdeClientTransaction(LPBYTE pData, DWORD cbData, HCONV hConv, HS
     {
     case XTYP_EXECUTE:
         /* Windows simply ignores hszItem and wFmt in this case */
+	if (pData == NULL)
+	{
+	    pConv->instance->lastError = DMLERR_INVALIDPARAMETER;
+	    return 0;
+	}
 	pXAct = WDML_ClientQueueExecute(pConv, pData, cbData);
 	break;
     case XTYP_POKE:

dlls/user32/tests/dde.c

@@ -433,10 +433,7 @@ todo_wine
     ret = DdeGetLastError(client_pid);
     ok(op == NULL, "Expected NULL, got %p\n", op);
     ok(res == 0xdeadbeef, "Expected 0xdeadbeef, got %d\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, topic);
     DdeFreeDataHandle(hdata);