register_meta function does not properly check variable type or key existence (of an array variable) before use

[chriscct7]

In the register_meta function, there are several cases where variables are allowed to be filtered, for example the $args parameter via the register_meta_args filter. However, once that filter is called, further down in the function, there are cases where the object type or existence of a key isn't checked before being used, allowing for a fatal error for example in the

if ( is_callable( $args['sanitize_callback'] ) ) { or if ( is_callable( $args['auth_callback'] ) ) { or if ( $has_old_sanitize_cb && is_callable( $args['sanitize_callback'] ) ) { lines

[ocean90]

Duplicate of #35658.

Patched in https://core.trac.wordpress.org/attachment/ticket/35658/35658.50.diff.