Fix performance regression from last commit

src/wcmf/lib/io/ImageUtil.php

@@ -396,11 +396,24 @@ private static function resizeImage($sourceFile, $destFile, $width, $type=null,
    * @return boolean
    */
   private static function isAnimated($imageFile) {
-    if (!FileUtil::fileExists($imageFile)) {
+    if (!($fh = @fopen($imageFile, 'rb'))) {
       return false;
     }
-    $manager = self::getImageManager();
-    return $manager->read($imageFile)->isAnimated();
+    $count = 0;
+    // An animated gif contains multiple "frames", with each frame having a header made up of:
+    // * a static 4-byte sequence (\x00\x21\xF9\x04)
+    // * 4 variable bytes
+    // * a static 2-byte sequence (\x00\x2C) (some variants may use \x00\x21 ?)
+
+    // We read through the file til we reach the end of the file, or we've found
+    // at least 2 frame headers
+    while (!feof($fh) && $count < 2) {
+      $chunk = fread($fh, 1024 * 100); //read 100kb at a time
+      $count += preg_match_all('#\x00\x21\xF9\x04.{4}\x00(\x2C|\x21)#s', $chunk, $matches);
+    }
+
+    fclose($fh);
+    return $count > 1;
   }
 
   /**