games/quake2max: fix known security and "missing return" issues

• Backport modified security patch from `games/quake2lnx' port
• Fix several -Werror=return-type bugs, the most important being the one in R_Init() function which prevented correct graphics initialization, causing the game to segfault during start-up
• For strlwr() function, just change it to `void' as its return value is never used anyway
• While here, add some places of interest to the WWW line

Reported by: Sergey V. Dyatko