Always return a value in Plugin_Upgrader::deactivate_plugin_before_upgrade(). Props jdgrimes. Fixes #29088.

git-svn-id: https://develop.svn.wordpress.org/trunk@30761 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/includes/class-wp-upgrader.php

@@ -1036,6 +1036,8 @@ class Plugin_Upgrader extends WP_Upgrader {
 			//Deactivate the plugin silently, Prevent deactivation hooks from running.
 			deactivate_plugins($plugin, true);
 		}
+
+		return $return;
 	}
 
 	/**