termux-job-scheduler hangs indefinitely when scheduling a new job

[xalexalex]

Problem description
termux-job-scheduler is unable to schedule a job, and hangs when I try to.

Steps to reproduce

cat > ~/script <<EOF
#!/data/data/com.termux/files/usr/bin/bash
termux-notification --content "$(date)"
EOF
chmod +x ~/script
termux-job-scheduler --script ~/script --period-ms 1800000

Expected behavior
script is scheduled to run every 30m ± 5m and termux-job-scheduler exits.

Actual behavior
the script runs once, but termux-job-scheduler hangs. termux-job-scheduler --pending run in another session doesn't output anything.

Additional information
termux-info:

Updatable packages:
All packages up to date
Subscribed repositories:
https://dl.bintray.com/grimler/science-packages-24 science/stable
https://dl.bintray.com/grimler/game-packages-24 games/stable
https://dl.bintray.com/termux/termux-packages-24 stable/main
System information:
Linux localhost 4.4.23+ #1 SMP PREEMPT Tue Jun 12 17:03:20 CST 2018 aarch64 Android
Termux-packages arch:
aarch64
Android version:
9
Device manufacturer:
HUAWEI
Device model:
PRA-LX1

Log: log-adb.txt

[xalexalex]

On further examination, apparently the hang is due to the lack of an explicit --network option, because despite termux-job-scheduler -h saying that the default for --network is "none", JobSchedulerApi.java does not handle the case where networkType == null.

I submitted a PR which adds handling for this case, with a default of "any" (which I think is more sensible than the default "none", however feel free to change that).