[PATCH] ntdll: Fix a memory leak (Valgrind).

[Jiangyi Chen]

==15674== 82 bytes in 1 blocks are definitely lost in loss record 1,041 of 2,256
==15674==    at 0x7BC6F0DA: notify_alloc (heap.c:260)
==15674==    by 0x7BC731BB: RtlAllocateHeap (heap.c:1725)
==15674==    by 0x7BCA3BC2: RtlCreateUnicodeString (rtlstr.c:239)
==15674==    by 0x7BC63CEA: get_image_path (env.c:720)
==15674==    by 0x7BC6583E: init_user_process_params (env.c:1450)