Function md5() always return non-empty-string.

[janbarasek]

Bugfix https://phpstan.org/r/cd56be9e-06f0-4474-98ce-360bb208a197

Sample:

<?php declare(strict_types = 1);

class HelloWorld
{
	/**
	* @return non-empty-string
	 */
	public function getHash(string $foo): string
	{
		return md5($foo);
	}
}

[ondrejmirtes]

Thank you!