proxy: mcplib_request_token() doesn't delimit the final token in a request
proxy: mcplib_request_token() doesn't delimit the final token in a request

mcplib_request_token() allows us to parse each token in a request string. The
existing implementation delimits tokens using <whitespace>. This approach
works for every token but the last one which will be followed by \r\n.

This patch uses the token offsets present within the request parser to calculate
the token boundaries instead of looping until the next delimiter.

memcached/memcached,memcached/memcached,memcached/memcached,memcached/memcached,dormando/memcached,dormando/memcached,dormando/memcached,memcached/memcached,dormando/memcached,dormando/memcached