Refactor "if" condition for "$_FILES" array

remove unnecessary nested if condition to one liner using AND Boolean operator.

upload.php

@@ -26,27 +26,25 @@ if (login()) {
         mkdir($dir, 0755, true);
     }
 
-    if (isset($_FILES)) {
-        if (isset($_FILES['file'])) {
-            $tmp_name = $_FILES['file']['tmp_name'];
-            $name     = basename($_FILES['file']['name']);
-            $error    = $_FILES['file']['error'];
-            $path     = $dir . $timestamp . '-' . $name;
-		
-            $check = getimagesize($tmp_name);
-		
-            if($check !== false) {
-                if ($error === UPLOAD_ERR_OK) {
-                    $extension = pathinfo($name, PATHINFO_EXTENSION);
-                    if (!in_array(strtolower($extension), $whitelist)) {
-                        $error = 'Invalid file type uploaded.';
-                    } else {
-                        move_uploaded_file($tmp_name, $dir . $timestamp . '-' . $name);
-                    }
+    if (isset($_FILES) && isset($_FILES['file'])) {
+        $tmp_name = $_FILES['file']['tmp_name'];
+        $name     = basename($_FILES['file']['name']);
+        $error    = $_FILES['file']['error'];
+        $path     = $dir . $timestamp . '-' . $name;
+	
+        $check = getimagesize($tmp_name);
+	
+        if($check !== false) {
+            if ($error === UPLOAD_ERR_OK) {
+                $extension = pathinfo($name, PATHINFO_EXTENSION);
+                if (!in_array(strtolower($extension), $whitelist)) {
+                    $error = 'Invalid file type uploaded.';
+                } else {
+                    move_uploaded_file($tmp_name, $dir . $timestamp . '-' . $name);
                 }
-            } else {
-                $error = "File is not an image.";
             }
+        } else {
+            $error = "File is not an image.";
         }
     }
 
@@ -61,4 +59,4 @@ if (login()) {
 } else {
     $login = site_url() . 'login';
     header("location: $login");
-}
+}