Check for argc==0 when calling wtokensplit()

Check for argc==0 when calling wtokensplit()

The WINGs-function wtokensplit does not set argv to NULL if no string has been
split - instead argc is set to 0.

You can only observe this issue if you compile Window Maker without any
optimization:

compile Window Maker with CFLAGS=""
run Window Maker and save a session
change session-file and replace a 'command xyz' line with 'command " "'
restart Window Maker
watch "Fatal error"-message

Retrieved-from: http://paldium.homeunix.org/tobias/wmaker/
Submitted-by: Gilbert Ashley <amigo@ibiblio.org>