[PATCH] Shellpkg/editor: Fix a bug that may modifies Line[-1]

[Ruiyu Ni <ruiyu.ni@intel.com>]

The original code as below intend to set the character
before last column to CHAR_NULL.
  Line[(LastCol % (ARRAY_SIZE (Line) - 1)) - 1] = CHAR_NULL;

But when LastCol % (ARRAY_SIZE (Line) - 1)) equals to 0,
Line[-1] is modified.

We should change to code as below:
  Line[(LastCol - 1) % (ARRAY_SIZE (Line) - 1)] = CHAR_NULL;

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Jaben Carsey <jaben.carsey@intel.com>
Cc: Hao A Wu <hao.a.wu@intel.com>
---
 .../Library/UefiShellDebug1CommandsLib/UefiShellDebug1CommandsLib.c     | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/ShellPkg/Library/UefiShellDebug1CommandsLib/UefiShellDebug1CommandsLib.c b/ShellPkg/Library/UefiShellDebug1CommandsLib/UefiShellDebug1CommandsLib.c
index d26d08f95c..b45e9a33f3 100644
--- a/ShellPkg/Library/UefiShellDebug1CommandsLib/UefiShellDebug1CommandsLib.c
+++ b/ShellPkg/Library/UefiShellDebug1CommandsLib/UefiShellDebug1CommandsLib.c
@@ -205,7 +205,7 @@ EditorClearLine (
         //
         // if CHAR_NULL is still at position LastCol, it will cause first line error
         //
-        Line[(LastCol % (ARRAY_SIZE (Line) - 1)) - 1] = CHAR_NULL;
+        Line[(LastCol - 1) % (ARRAY_SIZE (Line) - 1)] = CHAR_NULL;
       } else {
         Line[LastCol % (ARRAY_SIZE (Line) - 1)] = CHAR_NULL;
       }
-- 
2.12.2.windows.2