Explain the lack of +3/7

Originally committed as revision 16380 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/h264_parser.c

@@ -45,6 +45,9 @@ int ff_h264_find_frame_end(H264Context *h, const uint8_t *buf, int buf_size)
     for(i=0; i<buf_size; i++){
         if(state==7){
 #ifdef HAVE_FAST_UNALIGNED
+        /* we check i<buf_size instead of i+3/7 because its simpler
+         * and there should be FF_INPUT_BUFFER_PADDING_SIZE bytes at the end
+         */
 #    ifdef HAVE_FAST_64BIT
             while(i<buf_size && !((~*(uint64_t*)(buf+i) & (*(uint64_t*)(buf+i) - 0x0101010101010101ULL)) & 0x8080808080808080ULL))
                 i+=8;