User proper ellipsis char

As stated in
https://github.com/profanity-im/profanity/pull/1820#issuecomment-1498083383
profanity uses "..." (three dots) in a lot of places instead the proper
ellipsis char "…".

src/xmpp/iq.c

@@ -2596,7 +2596,7 @@ static int
 _mam_buffer_commit_handler(xmpp_stanza_t* const stanza, void* const userdata)
 {
     ProfChatWin* chatwin = (ProfChatWin*)userdata;
-    // Remove the "Loading messages ..." message
+    // Remove the "Loading messages …" message
     buffer_remove_entry(((ProfWin*)chatwin)->layout->buffer, 0);
     chatwin_db_history(chatwin, NULL, NULL, TRUE);
     return 0;