TinyMCE: add min-width to the placeholder images for the more and nextpage tags to fix them in themes that force width = auto.

Fixes #33022.

git-svn-id: https://develop.svn.wordpress.org/trunk@33351 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/js/tinymce/skins/wordpress/wp-content.css

@@ -144,6 +144,7 @@ img[data-mce-selected]::selection {
 	-webkit-box-shadow: none;
 	box-shadow: none;
 	width: 96%;
+	min-width: 96%;
 	height: 16px;
 	display: block;
 	margin: 15px auto 0;