Erroneous saved state behavior with SWIPL variable set but null.

[7heo]

When saving a state via the command

$ swipl -o mystate --foreign=save -c load.pl

The command

$ env SWIPL= ./mystate

errors out with:

./mystate: 3: exec: -x: not found

It is instead expected to start ProLog the same way as

$ ./mystate