[mod_webdav] If-None-Match on non-existent entity

fix logic inversion on If-None-Match test on non-existent entity

return 412 if If-None-Match: "*" for non-existent entity

x-ref:
  "trying to use Joplin Android App with lighttpd"
  https://redmine.lighttpd.net/boards/3/topics/10193

src/mod_webdav.c

@@ -2268,7 +2268,7 @@ webdav_if_match_or_unmodified_since (request_st * const r, struct stat *st)
 
     if (NULL != inm) {
         if (NULL == st
-            ? !buffer_eq_slen(inm, CONST_STR_LEN("*"))
+            ? buffer_eq_slen(inm, CONST_STR_LEN("*"))
               || (errno != ENOENT && errno != ENOTDIR)
             : http_etag_matches(etagb, inm->ptr, 1))
             return 412; /* Precondition Failed */