Bugfix: zsh crashes if invoked with unset PATH

[hzoli@xxxxxxxxxx (Zoltan Hidvegi)]

If PATH is not set in the environment, zsh dumps core the first time it
attempts to execute an external command without an absolute path. That is
because in init.c newcmdnamtable() is called before the path is initialised.

% unset PATH ; ./zsh -fc 'ls'            
zsh: 5275 segmentation fault (core dumped)  ./zsh -fc 'ls'

Because of this bug one of my boot scripts faild (that's almost the only place
where PATH is unset).

Here is the patch to fix that. It applies with fuzz 2 to the baseline zsh as I
added /usr/local/bin to the default path in my release.

Bye,
  Zoltan