avformat/smoothstreaming: Fix memleaks on errors

If an AVFormatContext could be allocated, but white-/blacklists couldn't
be copied, the AVFormatContext would leak as it was only accessible
through a local variable that goes out of scope when one goes to fail.

Furthermore, in case writing a header of a submuxer failed, the options
used for said call could leak.

Both of these memleaks have been fixed.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit abbb466368)
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavformat/smoothstreamingenc.c

@@ -331,12 +331,11 @@ static int ism_write_header(AVFormatContext *s)
             goto fail;
         }
 
-        ctx = avformat_alloc_context();
+        os->ctx = ctx = avformat_alloc_context();
         if (!ctx || ff_copy_whiteblacklists(ctx, s) < 0) {
             ret = AVERROR(ENOMEM);
             goto fail;
         }
-        os->ctx = ctx;
         ctx->oformat = oformat;
         ctx->interrupt_callback = s->interrupt_callback;
 
@@ -356,12 +355,13 @@ static int ism_write_header(AVFormatContext *s)
 
         av_dict_set_int(&opts, "ism_lookahead", c->lookahead_count, 0);
         av_dict_set(&opts, "movflags", "frag_custom", 0);
-        if ((ret = avformat_write_header(ctx, &opts)) < 0) {
+        ret = avformat_write_header(ctx, &opts);
+        av_dict_free(&opts);
+        if (ret < 0) {
              goto fail;
         }
         os->ctx_inited = 1;
         avio_flush(ctx->pb);
-        av_dict_free(&opts);
         s->streams[i]->time_base = st->time_base;
         if (st->codecpar->codec_type == AVMEDIA_TYPE_VIDEO) {
             c->has_video = 1;