arogue7: prevent segfaults when backstabbing while empty-handed. The calculation of the backstabbing multiplier checked the current weapon's properties without making sure the current weapon pointer was not NULL.

[Desktop Entry]
Encoding=UTF-8
Name=Rogue
GenericName=Rogue
Comment=The original curses-based adventure game
Exec=rogue
Icon=rogue.png
Terminal=true
Type=Application
Categories=Game;RolePlaying;
Version=1.0