Fix segmentation fault & add PORT argument to make http-launch more flexible

The segmentation fault was easily triggered by just using vlc 2.1.4. I imagine it sent some useless initial messages, which lead to a buffer overflow since the while-loop condition was not taking into account that we were iterating over the tmp array.

The port argument is straightforward and is simply intended to make it easy to run multiple http-launch on the same machine :)