Query: Remove nextpage block delimiters when setting up global post d…

…ata.

`WP_Query::setup_postdata()` splits the post up by `<!--nextpage-->`, which causes invalid block data to be contained in the post content.

This change removes the `<!-- wp:nextpage -->` and `<!-- /wp:nextpage -->`, as well.

Props pento, youknowriad, azaozz, noisysocks.
See #45401.



git-svn-id: https://develop.svn.wordpress.org/branches/5.0@43940 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/class-wp-query.php

@@ -4000,6 +4000,10 @@ public function setup_postdata( $post ) {
 			$content = str_replace( "\n<!--nextpage-->", '<!--nextpage-->', $content );
 			$content = str_replace( "<!--nextpage-->\n", '<!--nextpage-->', $content );
 
+			// Remove the nextpage block delimiters, to avoid invalid block structures in the split content.
+			$content = str_replace( '<!-- wp:nextpage -->', '', $content );
+			$content = str_replace( '<!-- /wp:nextpage -->', '', $content );
+
 			// Ignore nextpage at the beginning of the content.
 			if ( 0 === strpos( $content, '<!--nextpage-->' ) )
 				$content = substr( $content, 15 );