ffserver: Fix a null pointer dereference as a result of the FF_API_MAX_STREAMS cleanup.

Fixed another dereference in the RTSP code.

Removed a useless variable.

Changed an unnecessary looping assignment to a simple assignment suggested by
Maksym.

Added fixes and tweaks suggested by Maksym Veremeyenko [verem@m1stereo.tv] and
Clément B.

ffmpeg.c

@@ -673,6 +673,7 @@ static int read_ffserver_streams(AVFormatContext *s, const char *filename)
         return err;
     /* copy stream format */
     s->nb_streams = 0;
+    s->streams = av_mallocz(sizeof(AVStream *) * ic->nb_streams);
     for(i=0;i<ic->nb_streams;i++) {
         AVStream *st;
         AVCodec *codec;