ffmpeg: check av_opt_set_dict() return

Fixes CID1224275
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

ffmpeg.c

@@ -2864,7 +2864,11 @@ static int transcode_init(void)
                 av_log(NULL, AV_LOG_WARNING, "The bitrate parameter is set too low."
                                              " It takes bits/s as argument, not kbits/s\n");
         } else {
-            av_opt_set_dict(ost->enc_ctx, &ost->encoder_opts);
+            if (av_opt_set_dict(ost->enc_ctx, &ost->encoder_opts) < 0) {
+                av_log(NULL, AV_LOG_FATAL,
+                    "Error setting up codec context options.\n");
+                exit_program(1);
+            }
         }
 
         ret = avcodec_copy_context(ost->st->codec, ost->enc_ctx);