Font file cannot be found on unix system because auf case sensitivity

[kevinglier]

On linux systems there is a problem with font file names when the path does contain capitalised characters.

Is there a reason for the strtolower in this line?

https://github.com/tecnickcom/TCPDF/blob/d4adef47ca21c90e6483d59dcb9e5b1023696937/tcpdf.php#L9114