SIGABRT when TMPDIR does not exist

[asomers]

On FreeBSD 12-CURRENT, I accidentally tried running Kyua with TMPDIR pointing to a nonexistent path. It aborts every time. I don't even need to run a test; simply listing tests is sufficient.

[alans@stealthy /usr/tests]$ TMPDIR=/nonexistent kyua list
*** Fatal signal 6 received
*** Log file is /usr/home/alans/.kyua/logs/kyua.20171205-221254.log
*** Please report this problem to kyua-discuss@googlegroups.com detailing what you were doing before the crash happened; if possible, include the log file mentioned above
Abort trap
[alans@stealthy /usr/tests]$ kyua about
kyua (Kyua) 0.13

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