check if data was recieved

upload.php

@@ -28,6 +28,12 @@ function isZipFile($file)
 $mapId = generateMapId(); // the id of the map
 
 $map = $_FILES["map"]; // the file to upload
+
+if (!isset($map)) { // if the file is not set
+  echo "No file was uploaded";
+  die();
+}
+
 $file = $map["tmp_name"]; // the temporary file path
 $size = $map["size"]; // the size of the file