livehttp: use ChainLastAppend and remove ChainGather to gain speed

ChainGather in this case would make high amount of small memcopies which
kill performance quite nicely. Also ChainAppend would seek long list of
blocks everytime.

This basicly reverts 609a5fe2 and adds
ChainLastAppend. Overall speeding up livehttp-output quite a lot.

Reported-by: JEEB

modules/access_output/livehttp.c

@@ -188,6 +188,7 @@ struct sout_access_out_sys_t
     size_t  i_seglen;
     float   f_seglen;
     block_t *block_buffer;
+    block_t **last_block_buffer;
     int i_handle;
     unsigned i_numsegs;
     unsigned i_initial_segment;
@@ -234,6 +235,7 @@ static int Open( vlc_object_t *p_this )
     /* Try to get within asked segment length */
     p_sys->i_seglenm = CLOCK_FREQ * p_sys->i_seglen;
     p_sys->block_buffer = NULL;
+    p_sys->last_block_buffer = &p_sys->block_buffer;
 
     p_sys->i_numsegs = var_GetInteger( p_access, SOUT_CFG_PREFIX "numsegs" );
     p_sys->i_initial_segment = var_GetInteger( p_access, SOUT_CFG_PREFIX "initial-segment-number" );
@@ -761,6 +763,7 @@ static void Close( vlc_object_t * p_this )
     sout_access_out_sys_t *p_sys = p_access->p_sys;
     block_t *output_block = p_sys->block_buffer;
     p_sys->block_buffer = NULL;
+    p_sys->last_block_buffer = &p_sys->block_buffer;
 
     while( output_block )
     {
@@ -795,6 +798,7 @@ static void Close( vlc_object_t * p_this )
     {
         block_ChainRelease( p_sys->block_buffer );
         p_sys->block_buffer = NULL;
+        p_sys->last_block_buffer = &p_sys->block_buffer;
     }
 
     closeCurrentSegment( p_access, p_sys, true );
@@ -949,8 +953,9 @@ static int CheckSegmentChange( sout_access_out_t *p_access, block_t *p_buffer )
 static ssize_t writeSegment( sout_access_out_t *p_access )
 {
     sout_access_out_sys_t *p_sys = p_access->p_sys;
-    block_t *output = p_sys->block_buffer ? block_ChainGather( p_sys->block_buffer ) : NULL;
+    block_t *output = p_sys->block_buffer;
     p_sys->block_buffer = NULL;
+    p_sys->last_block_buffer = &p_sys->block_buffer;
     ssize_t i_write=0;
     bool crypted = false;
     while( output )
@@ -1045,7 +1050,7 @@ static ssize_t Write( sout_access_out_t *p_access, block_t *p_buffer )
 
         p_temp = p_buffer->p_next;
         p_buffer->p_next = NULL;
-        block_ChainAppend( &p_sys->block_buffer, p_buffer );
+        block_ChainLastAppend( &p_sys->last_block_buffer, p_buffer );
         p_buffer = p_temp;
     }