May I offer the following patch under consideration.  In addition to the
invalid free() it should fix the following problems as well:

1. trailing slash makes parsing the port number fail
2. if you leave out the optional port number, the proxy setup is silently
   skipped

AIUI, in its present form the only format that is properly recognized is:

http://host:port

After this patch, also the following should work as expected:

http://host:port/
http://host/      -- will use default HTTP port 80
http://host       -- will use default HTTP port 80

The port 80 is hardcoded; if one wants to be meticulous, one should probably
consider using getservent() instead.