fix(chatwin): Fix LMC autocompletion to suggest corrected message content

- Modified chatwin_outgoing_msg to call _chatwin_set_last_message for corrected messages, using replace_id per XEP-0308.
- Updated _chatwin_set_last_message to skip redundant and invalid free/strdup for same pointers.
- Added null checks in _chatwin_set_last_message for safety.
- Fixes autocompletion suggesting original message content instead of corrected content.

Fixes #24

tests/functionaltests/test_message.c

@@ -27,6 +27,9 @@ message_send(void **state)
     assert_true(prof_output_regex("me: .+Hi there"));
 }
 
+// TODO: `/message correct` XEP-0308 compliance (whether each correction links to the original message ID)
+// https://xmpp.org/extensions/xep-0308.html#rules
+
 void
 message_receive_console(void **state)
 {