fix(messages): no trailing newline for inputlist, tselect, z= with ext_messages

Problem:  Various list commands end in a newline to go to a new line on
          the message grid for the prompt message, which is unwanted
          with ext_messages.
Solution: Don't emit a trailing newline with ext_messages for
          inputlist(), :tselect and z=.

Co-authored-by: Tomasz N <przepompownia@users.noreply.github.com>

src/nvim/spellsuggest.c

@@ -588,7 +588,9 @@ void spell_suggest(int count)
         msg_advance(30);
         msg_puts(IObuff);
       }
-      msg_putchar('\n');
+      if (!ui_has(kUIMessages) || i < sug.su_ga.ga_len - 1) {
+        msg_putchar('\n');
+      }
     }
 
     cmdmsg_rl = false;