Upgrade/Install: Make sure `translate_level_to_role()` always returns a value.

Props diddledan.
Fixes #46848.
Built from https://develop.svn.wordpress.org/trunk@45747


git-svn-id: http://core.svn.wordpress.org/trunk@45558 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/includes/upgrade.php

@@ -3171,6 +3171,7 @@ function translate_level_to_role( $level ) {
 		case 1:
 			return 'contributor';
 		case 0:
+		default:
 			return 'subscriber';
 	}
 }

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.3-alpha-45746';
+$wp_version = '5.3-alpha-45747';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.