Deletion of unnecessary checks before two function calls

* [The function "free"](http://stackoverflow.com/questions/18775608/free-a-null-pointer-anyway-or-check-first "Free a null pointer anyway or check first?") is documented in the way that no action shall occur for a passed null pointer. Redundant safety checks can be avoided.
* [The function "http_get_free"](https://github.com/clibs/clib/blob/a4b1a4c1261476c5513ffb3f2da5eb48eb2f9395/deps/http-get/http-get.c#L96 "http_get_free() function") performs also input parameter validation. It is therefore not needed that a function caller repeats a corresponding check.