Don't leak memory if wrong resource type is passed to proc_open

Don't leak memory if wrong resource type is passed to proc_open

proc_open can accept stream resources in the descriptorspec, like this:

    proc_open("command", array(0 => $resource), $pipes);

Previously, if a resource which was *not* of type "stream" was passed, proc_open would
return without freeing dynamically allocated memory. It's fixed now.