fix load ico

lib/load_ico.rb

@@ -2,6 +2,7 @@
 
 module LoadIco
   BI_RGB = 0
+  PNG_SIGNATURE = "\x89PNG".b
 
   module_function
 
@@ -42,6 +43,8 @@ module LoadIco
 
     raise ArgumentError, 'Unable to load' unless image_data_bytes && image_data_bytes.bytesize == best_entry[:size]
 
+    return Vips::Image.new_from_buffer(image_data_bytes, '') if image_data_bytes.start_with?(PNG_SIGNATURE)
+
     image = load_image_entry(image_data_bytes, best_entry[:width], best_entry[:height])
 
     raise ArgumentError, 'Unable to load' unless image