Make get_tok_str support NULL as second param.
Make get_tok_str support NULL as second param.

As was pointed out on tinycc-devel, many uses of get_tok_str gives as
second parameter the value NULL. However, that pointer was
unconditionally dereferenced in get_tok_ptr. This commit explicitely add
support for thas case.

code4game/tinycc,run4flat/tinycc,seyko2/tinycc,andrewchambers/tccmirror,gfwilliams/tinycc,gfwilliams/tinycc,avih/tinycc,mirror/tinycc,leeduhem/tinycc,andrewchambers/tccmirror,andrewchambers/tccmirror,gfwilliams/tinycc,metaeducation/tcc,leeduhem/tinycc,code4game/tinycc,andreiw/tinycc,alfonsokim/tinycc,run4flat/tinycc,andreiw/tinycc,rchandramouli/tinycc,code4game/tinycc,leeduhem/tinycc,mirror/tinycc,mingodad/tinycc,metaeducation/tcc,fstudio/tinycc,andrewchambers/tccmirror,gfwilliams/tinycc,leeduhem/tinycc,seyko2/tinycc,seyko2/tinycc,run4flat/tinycc,andreiw/tinycc,seyko2/tinycc,gfwilliams/tinycc,metaeducation/tcc,mingodad/tinycc,mingodad/tinycc,avih/tinycc,alfonsokim/tinycc,mirror/tinycc,fstudio/tinycc,avih/tinycc,rchandramouli/tinycc,avih/tinycc,run4flat/tinycc,alfonsokim/tinycc,fstudio/tinycc,seyko2/tinycc,metaeducation/tcc,alfonsokim/tinycc,mirror/tinycc,mingodad/tinycc,metaeducation/tcc,fstudio/tinycc,andrewchambers/tccmirror,rchandramouli/tinycc,run4flat/tinycc,alfonsokim/tinycc,leeduhem/tinycc,rchandramouli/tinycc,rchandramouli/tinycc,fstudio/tinycc