shell32: Always allocate a whole ITEMIDLIST structure.

Partially allocating a structure generates -Warray-bounds warnings
with GCC11. In this specific case, given the rounding in memory
allocators, would even not increase the effective allocated size.

Signed-off-by: Eric Pouech <eric.pouech@gmail.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>

dlls/shell32/pidl.c

@@ -1574,7 +1574,7 @@ LPITEMIDLIST _ILCreateDesktop(void)
     LPITEMIDLIST ret;
 
     TRACE("()\n");
-    ret = SHAlloc(2);
+    ret = SHAlloc(sizeof(*ret));
     if (ret)
         ret->mkid.cb = 0;
     return ret;