utils: Fix get_vars
utils: Fix get_vars

Commit 030b50c2 broke the POSTing of variables without any values, we
would segfault on the value subtoken being NULL. Fix this by making it
behave the way it did before the conversion to strtok_r.

If a variable has no value with it, store it as an empty string. How
this didn't get noticed at the time is a mystery.

Signed-off-by: Andrew Clayton <02e0a999c50b1f88df7a8f5a04e1b76b35ea6a88@opentechlabs.co.uk>

ac000/receiptomatic