mod_http_oauth2: Tweak formatting of log message No need to `or ""` anymore since Prosody rev e88db5668cfb (0.11.0) and the %q format should produce either (nil) or "http://example"

This module blocks configured queries that change server state.

E.g. to make vCard storage read-only:

``` lua
readonly_stores = {
	vcard = { "vcard-temp", "vCard" };
}
```