MdeModulePkg/DxePrintLibPrint2Protocol: Fix incomplete print output

MdeModulePkg/DxePrintLibPrint2Protocol: Fix incomplete print output

This is caused by a previous patch which tried to fix string over-read.
It's found that that patch for PrintLib in MdePkg will cause premature
terminating of loop used to traversing format string and cause incomplete
string output. Because this library uses similar code to do the same
job, it has the same issue too. So the fix is also the same.

Cc: Liming Gao <liming.gao@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Jian J Wang <jian.j.wang@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>