Allow UploadedFile to be of size zero (#48)

Author: Zegnat

src/UploadedFileIntegrationTest.php

@@ -102,7 +102,7 @@ public function testGetSize()
 
         $file = $this->createSubject();
         $size = $file->getSize();
-        if ($size) {
+        if (false !== $size) {
             // @TODO remove when package require phpunit 9.1
             if (function_exists('PHPUnit\Framework\assertMatchesRegularExpression')) {
                 $this->assertMatchesRegularExpression('|^[0-9]+$|', (string) $size);