The UpdateArgcArgv() function documentation says "If OldArgv or OldArgc
is NULL then that value is not returned."
However, only OldArgc was checked for NULL, probably because of
copy-pasto. In case OldArgc was non-NULL, but OldArgv was null, it could
cause a segmentation fault.
Check OldArgv is not NULL before dereferencing the value.
Signed-off-by: Tormod Volden <debian.tormod@gmail.com>