[COMCTL32] Add NULL checks to SetWindowSubclass.

Imports Wine commit 04847e68f87 by Sven Baars.

Fixes crash in comctl32_winetest:subclass.

dll/win32/comctl32/commctrl.c

@@ -1266,6 +1266,9 @@ BOOL WINAPI SetWindowSubclass (HWND hWnd, SUBCLASSPROC pfnSubclass,
 
    TRACE ("(%p, %p, %lx, %lx)\n", hWnd, pfnSubclass, uIDSubclass, dwRef);
 
+    if (!hWnd || !pfnSubclass)
+        return FALSE;
+
    /* Since the window procedure that we set here has two additional arguments,
     * we can't simply set it as the new window procedure of the window. So we
     * set our own window procedure and then calculate the other two arguments