Hotfix for admincontroller.php (#1533)
Hotfix for admincontroller.php (#1533)

Now checking if 'content' is in $data. Some blueprints can have 'content' optional so not defined, which cause a crash when editing.
Checking with operator `??` and default value empty string `''`.
getgrav/grav-plugin-admin,getgrav/grav-plugin-admin,getgrav/grav-plugin-admin