#25 Fix for segfault on startup on AMD64 machines

[Richard Körber]

See bug 950010.

On AMD64 machines, Sodipodi 0.34 already segfaulted on
startup. The reason was an unsigned int which was later
used as signed, and caused a malloc with a gigantic
positive value. :)

Thanks to Matthieu Delahaye, who located the source
line that caused the segfault!

[Richard Körber]

fixes segfault on AMD64