avformat/http: Fix Out-of-Bounds access in process_line()

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 85f91ed760)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/http.c

@@ -871,7 +871,7 @@ static int process_line(URLContext *h, char *line, int line_count,
             while (av_isspace(*p))
                 p++;
             resource = p;
-            while (!av_isspace(*p))
+            while (*p && !av_isspace(*p))
                 p++;
             *(p++) = '\0';
             av_log(h, AV_LOG_TRACE, "Requested resource: %s\n", resource);