ShellPkg/ConsoleLogger: Fix a typo in UpdateDisplayFromHistory()

ShellPkg/ConsoleLogger: Fix a typo in UpdateDisplayFromHistory()

Within function UpdateDisplayFromHistory():

When getting a character with different attribute with the current one,
the statement to compare the character with a 'NULL' char should be:

*StringSegmentEnd != CHAR_NULL

rather than:

StringSegmentEnd != CHAR_NULL

This commit resolves this typo.

Cc: Jaben Carsey <jaben.carsey@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Hao Wu <hao.a.wu@intel.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>