Posts, Post Types: Increment post_count option value during blog creation.

Previously, the `post_count` option value was not incremented when the default "Hello world!" post is inserted during blog creation on a multisite installation.

Props henry.wright.
Fixes #54462.
See #53443.


git-svn-id: https://develop.svn.wordpress.org/trunk@52201 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/includes/upgrade.php

@@ -249,6 +249,9 @@ if ( ! function_exists( 'wp_install_defaults' ) ) :
 				'post_content_filtered' => '',
 			)
 		);
+
+		update_option( 'post_count', 1 );
+
 		$wpdb->insert(
 			$wpdb->term_relationships,
 			array(