Avoid leaking headers received from SSL proxy

Fixes part of 7816. Spotted by coverity. Fix on 0.2.2.1-alpha.

changes/bug7816_023

@@ -1,3 +1,7 @@
   o Minor bugfixes (memory leak, controller):
     - Fix a memory leak during safe-cookie controller authentication.
       Spotted by Coverity. Fixes part of bug 7816; bugfix on 0.2.3.13-alpha.
+
+  o Minor bugfixes (memory leak, HTTPS proxy support):
+    - Fix a memory leak when receiving headers from an HTTPS proxy.
+      Spotted by Coverity. Fixes part of bug 7816; bugfix on 0.2.1.1-alpha.

src/or/connection.c

@@ -1607,6 +1607,7 @@ connection_read_https_proxy_response(connection_t *conn)
     tor_free(headers);
     return -1;
   }
+  tor_free(headers);
   if (!reason) reason = tor_strdup("[no reason given]");
 
   if (status_code == 200) {