Posts: Don't modify post_name if it wasn't supplied to wp_insert_post().

Previously when updating a post using wp_insert_post(), post_name was 
regenerated based on post_title every time if post_name was not passed in 
explicitly. This irons out the expectation that properties not passed into the 
function should not be modified.

Props jason_the_adams. 
Fixes #34865.


git-svn-id: https://develop.svn.wordpress.org/trunk@35800 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/post.php

@@ -2872,7 +2872,8 @@ function wp_get_recent_posts( $args = array(), $output = ARRAY_A ) {
  *     @type string $ping_status           Whether the post can accept pings. Accepts 'open' or 'closed'.
  *                                         Default is the value of 'default_ping_status' option.
  *     @type string $post_password         The password to access the post. Default empty.
- *     @type string $post_name             The post name. Default is the sanitized post title.
+ *     @type string $post_name             The post name. Default is the sanitized post title
+ *                                         when creating a new post.
  *     @type string $to_ping               Space or carriage return-separated list of URLs to ping.
  *                                         Default empty.
  *     @type string $pinged                Space or carriage return-separated list of URLs that have
@@ -2953,6 +2954,9 @@ function wp_insert_post( $postarr, $wp_error = false ) {
 	$post_excerpt = $postarr['post_excerpt'];
 	if ( isset( $postarr['post_name'] ) ) {
 		$post_name = $postarr['post_name'];
+	} elseif ( $update ) {
+		// For an update, don't modify the post_name if it wasn't supplied as an argument.
+		$post_name = $post_before->post_name;
 	}
 
 	$maybe_empty = 'attachment' !== $post_type