Index: src/wp-admin/plugin-editor.php
===================================================================
--- src/wp-admin/plugin-editor.php	(revision 38260)
+++ src/wp-admin/plugin-editor.php	(revision )
@@ -36,9 +36,7 @@
 	exit;
 }
 
-if ( $file ) {
-	$plugin = $file;
-} elseif ( empty( $plugin ) ) {
+if ( ! isset( $plugin ) || empty( $plugin ) ) {
 	$plugin = array_keys($plugins);
 	$plugin = $plugin[0];
 }