Query: Check if $wp_query is set in query loop functions.

This avoids a PHP fatal error if any of these functions are called too early:

* `have_posts()`
* `in_the_loop()`
* `rewind_posts()`
* `the_post()`
* `have_comments()`
* `the_comment()`

bringing some consistency with conditional tags: `is_single()`, `is_home()`, etc.

This commit also removes unnecessary `return` from `the_comment()`, for consistency with `the_post()`. As `WP_Query::the_comment()` does not have a return value, this statement did not have any effect in practice.

Follow-up to [4934], [8807], [16947], [17068], [17083], [49147], [53395], [53396], [53400].

Props vdankbaar, thijso, teunvgisteren, timkersten655, SergeyBiryukov.
Fixes #55722.
Built from https://develop.svn.wordpress.org/trunk@53429


git-svn-id: http://core.svn.wordpress.org/trunk@53018 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.1-alpha-53428';
+$wp_version = '6.1-alpha-53429';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.