Crashes when Wifi connection lost during downloads

[Flo082002]

Exception

• User Action: ui error
• Request: App crash, UI failure
• Content Country: GB
• Content Language: en
• App Language: de_DE
• Service: none
• Version: 0.19.8
• OS: Linux Android 8.0.0 - 26

Crash log

java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.Thread.isAlive()' on a null object reference
	at us.shandian.giga.get.DownloadMission.joinForThreads(DownloadMission.java:816)
	at us.shandian.giga.get.DownloadMission.pauseThreads(DownloadMission.java:520)
	at us.shandian.giga.get.DownloadMission.notifyError(DownloadMission.java:362)
	at us.shandian.giga.get.DownloadMission.notifyError(DownloadMission.java:308)
	at us.shandian.giga.get.DownloadRunnable.run(DownloadRunnable.java:145)

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When I download videos and the Wifi connection gets lost, newpipe crashes.

[FireMasterK]

Could reproduce this on Android 10, here's the reproduction steps:

1. Start downloading something
2. While it's downloading, turn off your wifi and mobile data
3. Open the app and close it (not sure if necessary)
4. Turn on WiFi back on

Not too sure, but this may be blocked/fixed by #962

[NicolasToussaint]

If it helps, just reproduced this.
I switched WiFi connection less than a minute before the crash.

Exception

• User Action: ui error
• Request: ACRA report
• Content Country: GB
• Content Language: en-GB
• App Language: en_GB
• Service: none
• Version: 0.25.2
• OS: Linux Android 13 - 33

Crash log

java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.Thread.isAlive()' on a null object reference
	at us.shandian.giga.get.DownloadMission.joinForThreads(DownloadMission.java:814)
	at us.shandian.giga.get.DownloadMission.pauseThreads(DownloadMission.java:518)
	at us.shandian.giga.get.DownloadMission.notifyError(DownloadMission.java:360)
	at us.shandian.giga.get.DownloadMission.notifyError(DownloadMission.java:308)
	at us.shandian.giga.get.DownloadRunnable.run(DownloadRunnable.java:145)

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