WP_Query: Prevent get_queried_object() from returning false in author queries

[USERSATOSHI]

Prevents WP_Query::get_queried_object() from returning false in author queries. The documented return type is WP_Term|WP_Post_Type|WP_Post|WP_User|null, but get_userdata() can return false when passed a non-existent user ID or null.

Two scenarios caused false to leak out:

1. $this->queried_object_id stays null (no author resolved) -> get_userdata( null ) -> false
2. A non-existent author ID is set (e.g. ?author=999999) -> get_userdata( 999999 ) -> false

The fix guards both the get_userdata() call and its return value so $this->queried_object stays null in these edge cases, matching the documented return type.

Trac ticket: https://core.trac.wordpress.org/ticket/65400

Use of AI Tools

AI assistance: Yes
Tool(s): opencode (claude)
Model(s): deepseek-v4-flash-free
Used for: Tests.

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