*: Replace b_changedtick with new always-inline functions

Ref #8474

src/nvim/main.c

@@ -603,7 +603,7 @@ void getout(int exitval)
         }
 
         buf_T *buf = wp->w_buffer;
-        if (buf->b_changedtick != -1) {
+        if (buf_get_changedtick(buf) != -1) {
           apply_autocmds(EVENT_BUFWINLEAVE, buf->b_fname,
                          buf->b_fname, false, buf);
           buf_set_changedtick(buf, -1);  // note that we did it already