Avoid a PHP notice if the `last_updated` property isn't present in a plugin's data from the Plugins API.

Fixes #33024
Props icetee

Built from https://develop.svn.wordpress.org/trunk@34458


git-svn-id: http://core.svn.wordpress.org/trunk@34422 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/includes/plugin-install.php

@@ -457,7 +457,11 @@ function install_plugin_information() {
 	echo "</div>\n";
 
 	$date_format = __( 'M j, Y @ H:i' );
-	$last_updated_timestamp = strtotime( $api->last_updated );
+
+	if ( ! empty( $api->last_updated ) ) {
+		$last_updated_timestamp = strtotime( $api->last_updated );
+	}
+
 	?>
 	<div id="<?php echo $_tab; ?>-content" class='<?php echo $_with_banner; ?>'>
 	<div class="fyi">

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.4-alpha-34457';
+$wp_version = '4.4-alpha-34458';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.