ffmpeg: save two levels of indentation in flush_encoders()

By replacing
if (foo)
    <do stuff>

with
if (!foo)
    continue;
<do stuff>

ffmpeg.c

@@ -1451,17 +1451,17 @@ static void flush_encoders(int ist_index, OutputStream *ost_table, int nb_ostrea
 
     for (i = 0; i < nb_ostreams; i++) {
         OutputStream   *ost = &ost_table[i];
-
-        if (ost->source_index == ist_index) {
         AVCodecContext *enc = ost->st->codec;
         AVFormatContext *os = output_files[ost->file_index].ctx;
 
-            if(ost->st->codec->codec_type == AVMEDIA_TYPE_AUDIO && enc->frame_size <=1)
+        if (ost->source_index != ist_index || !ost->encoding_needed)
+            continue;
+
+        if (ost->st->codec->codec_type == AVMEDIA_TYPE_AUDIO && enc->frame_size <=1)
             continue;
-            if(ost->st->codec->codec_type == AVMEDIA_TYPE_VIDEO && (os->oformat->flags & AVFMT_RAWPICTURE))
+        if (ost->st->codec->codec_type == AVMEDIA_TYPE_VIDEO && (os->oformat->flags & AVFMT_RAWPICTURE))
             continue;
 
-            if (ost->encoding_needed) {
         for(;;) {
             AVPacket pkt;
             int fifo_bytes;
@@ -1528,8 +1528,6 @@ static void flush_encoders(int ist_index, OutputStream *ost_table, int nb_ostrea
             write_frame(os, &pkt, ost->st->codec, ost->bitstream_filters);
         }
     }
-        }
-    }
 }
 
 /* pkt = NULL means EOF (needed to flush decoder buffers) */