[PATCH] Silence a new Valgrind warning

Hi,

Commit 4966bd3ed95e revealed a non-critical memory leak in
ProcessStartupPacket() which Valgrind is very much upset about:

```
63 (32 direct, 31 indirect) bytes in 1 blocks are definitely lost in
loss record 355 of 800
at 0x9D260C: palloc (mcxt.c:1411)
by 0x54B3D2: new_list (list.c:137)
by 0x54B8CC: lappend (list.c:344)
by 0x78B41A: ProcessStartupPacket (backend_startup.c:786)
by 0x78A411: BackendInitialize (backend_startup.c:295)
by 0x789F2F: BackendMain (backend_startup.c:110)
by 0x67EEED: postmaster_child_launch (launch_backend.c:268)
by 0x685D50: BackendStartup (postmaster.c:3606)
by 0x6830CF: ServerLoop (postmaster.c:1713)
by 0x682982: PostmasterMain (postmaster.c:1403)
by 0x547DFE: main (main.c:231)
```

The proposed patch silences the warnings.

--
Best regards,
Aleksander Alekseev