ShellPkg: Fix copy-pasto in NULL check to prevent segfault

The documentation says "If OldArgv or OldArgc is NULL then that value is
not returned."

However, only OldArgc was checked for NULL. In case OldArgc was non-NULL,
but OldArgv was null, it would cause a segmentation fault.

Signed-off-by: Tormod Volden <[email protected]>

ShellPkg/Application/Shell/ShellParametersProtocol.c

@@ -1447,7 +1447,7 @@ UpdateArgcArgv (
     *OldArgc = ShellParameters->Argc;
   }
 
-  if (OldArgc != NULL) {
+  if (OldArgv != NULL) {
     *OldArgv = ShellParameters->Argv;
   }