lavc/bsf: fix memory leak after av_dict_parse_string fail

In case of failure, all the successfully set entries are stored in
*pm. We need to manually free the created dictionary to avoid
memory leak.
Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Jun Zhao <barryjzhao@tencent.com>

libavcodec/bsf.c

@@ -517,8 +517,8 @@ static int bsf_parse_single(const char *str, AVBSFList *bsf_lst)
 
     ret = av_bsf_list_append2(bsf_lst, bsf_name, &bsf_options);
 
-    av_dict_free(&bsf_options);
 end:
+    av_dict_free(&bsf_options);
     av_free(buf);
     return ret;
 }