ShellPkg: Use safe string functions to refine code.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Qiu Shumin <shumin.qiu@intel.com>
Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>


git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@17730 6f19259b-4bc3-4df7-8a09-765794883524

ShellPkg/Application/Shell/ShellEnvVar.c

@@ -339,7 +339,10 @@ SetEnvironmentVariables(
     //
     // Copy the string into the Key, leaving the last character allocated as NULL to terminate
     //
-    StrnCpy(Node->Key, CurrentString, StrStr(CurrentString, L"=") - CurrentString);
+    StrCpyS( Node->Key, 
+              StrStr(CurrentString, L"=") - CurrentString + 1, 
+              CurrentString
+              );
 
     //
     // ValueSize = TotalSize - already removed size - size for '=' + size for terminator (the last 2 items cancel each other)