fix: possible php error if redirect column is an empty string

[Tofandel]

[hafezdivandari]

This actually never happens, the redirect_uris column (if exists) is always a json array (may be emtpy []) but never null or '' unless you have manipulated the table manually, if so I suggest to have default value of [] for your previouse records instead of this PR.

[Tofandel]

This actually never happens
unless you have manipulated the table manually

So it can happen :) especially after a migration

This is just a very basic sanity check