Fix markup in wp-admin/themes.php. see #20403.

* Always print opening form tag.
* Always ensure table content clears to the next line. This prevents table content from bunching next to the 'Available Themes' headline, which occurred when only one theme was active on a multisite install.


git-svn-id: https://develop.svn.wordpress.org/trunk@20716 602fd350-edb4-49c9-b593-d223f7449a82

wp-admin/css/wp-admin.dev.css

@@ -7575,6 +7575,10 @@ h3 span {
 	line-height: 180%;
 }
 
+#filter-box {
+	clear: both;
+}
+
 .feature-filter {
 	padding: 8px 12px 0;
 }