Fix FTP module type and initializer defects surfaced by GCC 13

[midwan]

Building the OS3 target with GCC 13.4 (via stefanreinauer/amiga-gcc:gcc-v13.4) surfaced several latent defects in the FTP module that GCC 6.5 does not diagnose. No functional change intended.

Changes

Function pointer type mismatch (the one with teeth) — message_update() was declared taking struct message_update_info *, but every consumer types the callback as int (*)(void *, int, char *): the signature used by ftp_cwd(), connect_host(), login() and _getreply() in ftp.h, and by the updatefn/startupfn/cwdfn locals. Calling through a mismatched function pointer is undefined behaviour, and it was happening at five sites — ftp_lister.c:1004,1125,2051 and ftp_lister_connect.c:620,624.

Fixed at the definition so all five sites are well typed with no casts. Worth doing regardless of toolchain: GCC 14 rejects this outright, and mismatched indirect calls are a known hazard under -flto, which the OS3 build uses.

Always-true guard — lister_new_connection() tested cm->cm_opus && before dereferencing, but cm_opus is a char[] member so the test can never be false; cm itself is already checked one line above. Dead term removed.

Brace elision — systype_lookup()'s sys_types[] initialized an array of two-member structs from a flat list. Legal C and behaviourally correct, but fragile. Now braced per element.

struct timeval initializer — iread() used {0, 0}. The NDK 3.2 definition wraps both fields in anonymous unions (tv_sec/tv_secs, tv_usec/tv_micro), so the flat form warns. Changed to {0}, which is already the idiom at ftp.c:1213,1613,1867 and ftp_recursive.c:3477 — this line was the lone deviation.

Verification

Check	Result
GCC 6.5 (sacredbanana/amiga-compiler:m68k-amigaos) make os3 all debug=no	exit 0, no new warnings in touched files
GCC 13.4, the seven target warnings	all resolved; zero ftp_lister_connect.c warnings remain

CI exercises the GCC 6.5 path, which is what the regression build above covers.

Not included

A GCC 13 baseline over the whole codebase shows 261 unique warnings. Among them are 11 more -Waddress always-true tests of exactly the class fixed here — buffers_sort.c (8, lines 536-581), config_environment.c:1521, filetype.c:2290, ftp_main.c:1189. Each needs individual reading to tell whether the intended check was something else, so they are left for a follow-up rather than bundled in.