This lets a compound command like 'cd .. && echo ok' print 'ok',
similar to how most other shells behave.
* lisp/eshell/esh-cmd.el (eshell-exit-success-p): Only check if the
last exit code was zero, rather than first checking whether the last
command returned nil.
(eshell-exec-lisp): Set `eshell-last-command-status' to 1 on error.
Copyright-paperwork-exempt: yes
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