Automatic Updates: Add a rollback functionality upon installation failure, the rollback package will be available for partial-updates for automatic updates and be similar to our existing partial builds (but in reverse).

A further iteration of this is to also detect whitescreens (fatals) after a auto update, and trigger the rollback for that too.
See #22704


git-svn-id: https://develop.svn.wordpress.org/trunk@25649 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/includes/update.php

@@ -136,6 +136,8 @@ function get_core_checksums( $version ) {
 
 	// Cache the checksums for later
 	foreach ( $version as $v ) {
+		if ( ! isset( $body['checksums'][ $v ] ) )
+			$body['checksums'][ $v ] = false;
 		set_site_transient( "core_checksums_$v", $body['checksums'][ $v ], HOUR_IN_SECONDS );
 		$return[ $v ] = $body['checksums'][ $v ];
 	}