updated for version 7.3.051

Problem:    Crash when /home/mool/bin:/usr/local/sbin:/usr/local/bin:/home/mool/java/jdk/bin:/bin:/sbin:/usr/bin:/usr/games:/usr/sbin:/usr/X11R6/bin:/usr/local/linux-jdk1.3.1/bin:/usr/local/lib/python2.2/Tools/idle is empty.
Solution:   Check for vim_getenv() returning NULL. (Yasuhiro Matsumoto)