when has next line to draw, should not overwrite the BltX to 0, instead should keep the BltX value that pass into StringToImage function. Contributed-under: TianoCore Contribution Agreement 1.0 Signed-off-by: Dandan Bi <dandan.bi@intel.com> Reviewed-by: Eric Dong <eric.dong@intel.com> Reviewed-by: Liming Gao <liming.gao@intel.com> Acked-by: Laszlo Ersek <lersek@redhat.com>