MdePkg/BasePrintLib: Fix error in Precision position calculation
Due to a potential hole in the stop condition of loop, the two continuous
access to ArgumentString (index, index+1) inside the loop might cause the
string ending character ('\0') and the byte after it to be read.
Cc: Michael D Kinney <michael.d.kinney@intel.com> 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: Liming Gao <liming.gao@intel.com>