Fix the display of Audio and Video in the Media Library when using IE8 and below.

This delays the execution of instantiating of the MediaElement.js player until the render is complete, and the node is in the DOM.
Although it's a bug that this is needed in the first place, this will cover us until a new MediaElement.ks release is made.

Props afercia.
Fixes #31058 for 4.1.

Built from https://develop.svn.wordpress.org/branches/4.1@31444


git-svn-id: http://core.svn.wordpress.org/branches/4.1@31425 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/js/media-grid.js

@@ -298,7 +298,9 @@
 			media.mixin.removeAllPlayers();
 			this.$( 'audio, video' ).each( function (i, elem) {
 				var el = media.view.MediaDetails.prepareSrc( elem );
+				setTimeout( function() {
 					new MediaElementPlayer( el, media.mixin.mejsSettings );
+				}, 0 );
 			} );
 		}
 	});