Posts, Post Types: Ensure `is_page_template()` can only return true when viewing a singular post query.

Props natereist, dlh
Fixes #39211

Built from https://develop.svn.wordpress.org/trunk@39599


git-svn-id: http://core.svn.wordpress.org/trunk@39539 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/post-template.php

@@ -1631,6 +1631,10 @@ function get_the_password_form( $post = 0 ) {
  * @return bool True on success, false on failure.
  */
 function is_page_template( $template = '' ) {
+	if ( ! is_singular() ) {
+		return false;
+	}
+
 	$page_template = get_page_template_slug( get_queried_object_id() );
 
 	if ( empty( $template ) )

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.8-alpha-39598';
+$wp_version = '4.8-alpha-39599';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.