avformat/dashdec: Remove dead code

The code in question seems to have been copied from about 70 lines
above; yet the code here is only executed if some of the variables
(namely representation_segmenttemplate_node and fragment_template_node)
are NULL, so it makes no sense to check them for a child element.

Also remove a redundant resetting of a pointer to an AVFormatContext
after avformat_close_input() (which already sets the pointer to NULL).

Reviewed-by: Steven Liu <lq@chinaffmpeg.org>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavformat/dashdec.c

@@ -1047,12 +1047,7 @@ static int parse_manifest_representation(AVFormatContext *s, const char *url,
                 fragmenturl_node = xmlNextElementSibling(fragmenturl_node);
             }
 
-            fragment_timeline_node = find_child_node_by_name(representation_segmenttemplate_node, "SegmentTimeline");
-
-            if (!fragment_timeline_node)
-                fragment_timeline_node = find_child_node_by_name(fragment_template_node, "SegmentTimeline");
-            if (!fragment_timeline_node)
-                fragment_timeline_node = find_child_node_by_name(adaptionset_segmentlist_node, "SegmentTimeline");
+            fragment_timeline_node = find_child_node_by_name(adaptionset_segmentlist_node, "SegmentTimeline");
             if (!fragment_timeline_node)
                 fragment_timeline_node = find_child_node_by_name(period_segmentlist_node, "SegmentTimeline");
             if (fragment_timeline_node) {
@@ -1898,7 +1893,6 @@ static void close_demux_for_component(struct representation *pls)
     memset(&pls->pb, 0x00, sizeof(AVIOContext));
     pls->ctx->pb = NULL;
     avformat_close_input(&pls->ctx);
-    pls->ctx = NULL;
 }
 
 static int reopen_demux_for_component(AVFormatContext *s, struct representation *pls)