rawdec: fix mjpeg probing

There can be other headers than "Content-Type:" (in this case, a
"Content-Length:" header was following), so checking for a trailing
newline is wrong.

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit bf51fcd304)

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/rawdec.c

@@ -186,7 +186,7 @@ static int mjpeg_probe(AVProbeData *p)
     }
 
     if (nb_invalid*4 + 1 < nb_frames) {
-        static const char ct_jpeg[] = "\r\nContent-Type: image/jpeg\r\n\r\n";
+        static const char ct_jpeg[] = "\r\nContent-Type: image/jpeg\r\n";
         int i;
 
         for (i=0; i<FFMIN(p->buf_size - sizeof(ct_jpeg), 100); i++)