Fix some potential overflow issues (#1161)

Fix some potential overflow issues (#1161)

* Fix some potential overflow issues

Put sizeof to the beginning of the multiplication to enforce that
size_t instead of smaller integer types is used for the calculation.

This fixes warnings from LGTM:

    Multiplication result may overflow 'unsigned int'
    before it is converted to 'unsigned long'.

It also allows removing some type casts.

Signed-off-by: Stefan Weil <sw@weilnetz.de>
* Fix code indentation

Signed-off-by: Stefan Weil <sw@weilnetz.de>