Type error in FileUpload->getImageSize()

[dada-amater]

Version: 3.0.4

Bug Description

$file->getImageSize() returns TypeError for the file is not an image. PHP function getimagesize() returns array|false, not array|null.
See https://github.com/nette/http/blob/master/src/Http/FileUpload.php#L191

Steps To Reproduce

Upload a file that is not image and ask for $file->getImageSize().

Expected Behavior

No TypeError.

Possible Solution

Retype result of PHP function getimagesize() from false to null.