avcodec/ccaption_dec: default rollup to row 10

This ensures that captions are written towards the bottom of the screen
when tuning into mid-stream. The row will be reset on the receipt of the
next PAC command. Row 10 was chosen as it corresponds to the value of
"0" in a PAC (see row_map in handle_pac()).
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/ccaption_dec.c

@@ -261,6 +261,7 @@ static av_cold int init_decoder(AVCodecContext *avctx)
     /* taking by default roll up to 2 */
     ctx->mode = CCMODE_ROLLUP;
     ctx->rollup = 2;
+    ctx->cursor_row = 10;
     ret = ff_ass_subtitle_header(avctx, "Monospace",
                                  ASS_DEFAULT_FONT_SIZE,
                                  ASS_DEFAULT_COLOR,
@@ -298,7 +299,7 @@ static void flush_decoder(AVCodecContext *avctx)
     ctx->prev_cmd[1] = 0;
     ctx->mode = CCMODE_ROLLUP;
     ctx->rollup = 2;
-    ctx->cursor_row = 0;
+    ctx->cursor_row = 10;
     ctx->cursor_column = 0;
     ctx->cursor_font = 0;
     ctx->cursor_color = 0;