Comments: Fix "Show more comments" button for custom comment types.

The comments metabox assumed all comment `<tr>` elements carry the
`comment` class, which is not the case for custom comment types such as
WooCommerce reviews. Match rows by an id starting with `comment-`
instead, so regular comments and custom comment types are both counted.

Also correct the default number of comments requested in the AJAX call
from 20 to 10, aligning the frontend with the backend, which falls back
to 10. The mismatch made the frontend believe all comments were already
loaded when they were not.

Props Aljullu, PavloBorysenko, tyxla.
Fixes #65392.

git-svn-id: https://develop.svn.wordpress.org/trunk@62624 602fd350-edb4-49c9-b593-d223f7449a82

Author: tyxla

src/js/_enqueues/admin/post.js

@@ -35,13 +35,13 @@ window.wp = window.wp || {};
 		 * @memberof commentsBox
 		 *
 		 * @param {number} total Total number of comments for this post.
-		 * @param {number} num   Optional. Number of comments to fetch, defaults to 20.
+		 * @param {number} num   Optional. Number of comments to fetch, defaults to 10.
 		 * @return {boolean} Always returns false.
 		 */
 		get : function(total, num) {
 			var st = this.st, data;
 			if ( ! num )
-				num = 20;
+				num = 10;
 
 			this.st += num;
 			this.total = total;
@@ -97,7 +97,7 @@ window.wp = window.wp || {};
 		 * @param {number} total Total number of comments to load.
 		 */
 		load: function(total){
-			this.st = jQuery('#the-comment-list tr.comment:visible').length;
+			this.st = jQuery('#the-comment-list tr[id^="comment-"]:visible').length;
 			this.get(total);
 		}
 	};